Addressing Some Common Questions & Arguments

1. “They can’t even predict next week’s weather”/”Models are useless”

As Dr. William Connolley notes, weather and climate aren’t the same thing, and “predicting one isn’t the same as the other. Consider (analogy: not perfect but not bad) the shore of the ocean and the level of the sea: tides can be predicted with great accuracy years in advance; waves can’t be predicted any better than weather.”

Although it can ultimately be influenced by warming, weather is about short-term ocean-atmosphere dynamics and the movement of heat and moisture within the system. Global climate is a function of Earth’s longer term “energy budget” (sunlight in vs. infrared out), and whether there’s an overall change in heat and water vapor over time. Weather “noise” cancels out over time, revealing the “signal” of a changing climate in the longer-term averages. Today’s models haven’t been very good at consistently predicting fluctuations on weekly to inter-decadal timescales, and this is a source of denial. Climate models, though, have been much better at simulating the longer term trends.

Some people demonize models in general (a key tool in many areas of science and medicine), but what counts is how scientifically robust they are. Modern general circulation models are valuable for analyzing influences from greenhouse gases to solar flux, and for ‘climate’ they agree well with the real world at large to medium scales. They’re continuously validated (Example), and refined with the latest data and cutting-edge physics. Yet their indicated trends have persisted, and no model can account for those trends without including human-produced greenhouse gases. GCMs have done a good job of projecting average temperature change over time, the magnitude of volcanic cooling, the amplification of Arctic warming, an increase in heat waves and precipitation extremes, greater warming at night than during the day, patterns of ocean warming, and the stratospheric cooling effect (#24).

Still, as in any science we can’t expect perfection. Detailed projection (particularly of complex regional climates) is difficult. But models needn’t be exact to give an indication of a trend and it’s major effects. While there are uncertainties, recent research suggests models may inadequately assess amplifying feedbacks. That could make at least some longer term projections too conservative. Those who argue against climate concerns by pointing to uncertainties in models tend to ignore the possibility that they won’t turn out in our favor.


Climate models accurately predicted global warming when reflecting natural ocean cycles
* The Physics of Climate Modeling
* 1981 climate change predictions were eerily accurate
* Realclimate: Short and simple arguments for why climate can be predicted

2. “So what’s a few degrees?”

Contrarians take advantage of the public’s weather-oriented perspective when highlighting lower-end warming projections of “only” a few degrees. The IPCC fourth assessment, representing reviewed and assessed research, included a “best estimate” range of 1.8 – 4.0°C (3.24 – 7.2°F, Δ T) by 2100, with a potential range of 1.1 – 6.4°C (1.98 – 11.52°F). This is based on several scenarios, with the low end assuming a world with stabilized population and a quick transition from fossil fuels, and the top numbers assuming high emissions. Subsequent studies based on continuing emissions growth indicate a rise of 4-7 degrees C. One of the latest from Hadley Centre (here) suggests that on today’s path, we could see 4 degrees C as early as 2060.

Top climatologists view warming of about 2°C (3.6°F) this century as a hazard point, beyond which broadly disruptive changes become much more likely. This would be at least 40 times the estimated average warming rate of the paleocene-eocene thermal maximum about 56 million years ago (which was coming off a relatively warm-adapted biosphere, with little land-based ice to contribute to sea level rise).

Many studies suggest a “climate sensitivity” of around 3°C (5.4°F) for a doubling of pre-industrial CO2 (something that could easily occur without mitigation). The AR4 notes that it’s “likely to be in the range 2 to 4.5°C with a best estimate of about 3°C, and is very unlikely to be less than 1.5°C. Values substantially higher than 4.5°C cannot be excluded, but agreement of models with observations is not as good for those values.” More here.

For local weather, a single-digit change over decades may not seem like much, but a global average temperature increase of a few degrees is large, translating to stronger regional effects, including from concentrations of extra energy within the system. To help put things into perspective, the anomaly associated with early 20th century warmth was less than 1°F. The global mean temperature during the last glacial period was about 9°F lower than today’s, and much of that seems to have occurred more slowly. Since then, things have been relatively stable, aiding the development of agrarian societies.

Dr. Ray Pierrehumbert notes: “So far we haven’t quite gotten to 400ppm CO2, but we’ll eventually go to 700 or more without controls. We haven’t even seen the full warming effects of that 400ppm yet, because it takes time for the ocean to warm up. So, the striking thing is that it has already gotten to the point that the recent warming stands out from the natural variability of the past thousand years or more, despite the fact that so far we’ve only experienced the barest beginnings of the warming. That’s not just striking. It ought to be alarming.”

Dr. Tim Flannery: “Our deep psychological resistance to thinking that “warm” might be bad allows us to be deceived about the nature of climate change. Those who have exploited this human blind spot have left many people – even the well-educated – confused. This is the result of an unhealthy, in some instances corrupt, relationship between government and industry.”

People often do see warmth as “nice”, until winter ends or the warmth is accompanied by drought, ecological impacts, insect invasions, floods, changing croplands, more severe weather, or high wildfire danger.

3. “But the weather is downright chilly in ________/We hit a record low!”

Global warming refers to global average temperature change over time (an indicator of Earth’s “energy budget”: Energy in vs. energy radiated to space). It doesn’t mean constant, regionally synchronous change or the end of cold snaps. Despite the trend, fluctuations continue in a fluid-dynamic system, particularly from the variability in ocean heat exchange and heat distribution. These maps give some idea of how anomalies can vary on short timescales, especially regionally:


Vs. average anomaly for the past decade (despite a relaxing of the surface trend associated with shorter term influences):


Record highs will also occur more frequently with global warming (already observed, with record highs occurring about twice as often as record lows over the past decade), but local extremes alone are not necessarily global indicators. It can be interesting, though, to consider the circumstances under which records are set. Frequently anomalous warmth despite the cooling influence of la niña, increased Asian emissions of sulfur particulates, and a deep solar minimum could be viewed differently from past warm spells under the opposite conditions.

An example of a trend in record temperature ratios, expected to accelerate:

And when we look at the global averages, most of the warmest years are in the past decade:

Still, the weather we observe is a confluence of both natural variability (such as from ocean cycles) and the cumulative human influence. And perceptions can mislead. People don’t think of global mean temperature being on the rise when they’re in the middle of a winter storm. Many regions experience frosty spring weather, and lingering snowfall can give a strong impression of cold even when temperatures aren’t unusually low. And under favorable conditions, water vapor feedback from a warming planet can make regional snow & ice events more intense, via the mixing of moist air.

4. “Climate change is normal/has happened throughout Earth’s history”/”CO2 has been higher before”

Past events do nothing to support the idea that today’s ongoing process is mostly natural, or irrelevant to Earth’s present ecology. Although there are generally modest holocene fluctuations from things like sulfates, solar cycles, and El Niño/La Niña oscillations, warming from the carbon imbalance is on top of those. Significant global-scale changes in the past have generally occurred over millennia (instability related to glacial period termination being an exception), allowing life to adapt or migrate. Warming from unabated emissions will likely be much stronger, more widespread and more persistent than anything seen by civilization. Without this, Earth may well have thousands of years more of mostly stable, mild climate (see below).

As for CO2, there have been periods in pre-history with higher concentrations, but other aspects of the Earth system were starkly different (and a big issue today is the rate of change, from a relatively moderate baseline). There were even periods of relatively high CO2 when temperatures weren’t as warm as one would expect. That’s due to climate factors like solar irradiance, which was lower and has slowly risen over millions of years (some fascinating detail here). If we could go back in time and double Earth’s CO2 concentrations (which we’re poised to do without serious mitigation), that would have consequences. But not the exact same consequences as ratcheting up CO2 levels in what is now considered roughly the middle of the holocene.

5. “But most of the warming occurred before 1940″/”What about past events like the medieval warm period?”, and “Isn’t Earth just recovering from the ‘Little Ice Age’?”

The first point is misleading and incorrect. NASA notes that “More specifically, there was slow global warming, with large fluctuations, over the century up to 1975 and subsequent rapid warming of almost 0.2°C per decade.” Despite some regionally concentrated heat, events of the 1930’s were much less significant globally than the recent trend (example: 1930’s vs. the 1990’s & beyond), and were likely related to  a period of moderately higher solar activity, with oceanic heat distribution helping determine local effects.Greenland (so-named to attract colonists, when most of it wasn’t green) hasn’t always been representative of major global trends, but change there had been limited in scope during recorded history. And today’s situation is still progressing. Dr. Raymond Bradley of the UMASS Climate System Research Center notes that “human activity is pushing warming at a much faster rate than in the past”, and NASA’s Evelyne Yohe notes that the Arctic warmth of the early 1930’s was the result of three decades of gradual warming. Even the change of the past decade or so has exceeded that.Research indicates that the “Medieval Warm Period” (and the moderate cooling dubbed the “Little Ice Age”) was comprised of non-synchronous regional changes, and had relatively little impact on the global averages. It also occurred over centuries (more detail on it here). The 2007 AR4 references proxy studies, independent of the “hockey stick” (links bar), affirming that the global magnitude of medieval warmth was weaker than that of today. Dr. Michael Mann also addresses this here (and for an example of a contrarian trick that makes it appear otherwise, or that the current trend is part of a natural cycle, see sidebar). The “mid-holocene warm period”, about 6000 years ago, is a similar story, with high-latitude seasonal warmth.It has even been suggested that the trend is part of a recovery from the “little ice age”. Not only does evidence suggest it wasn’t a globally synchronous event either, but a trend can’t be called a recovery if natural mechanisms can’t account for it (see below).

6. “The temperature record is too short to suggest human influence”

The determination of anomalous global change, and the expectation that it will worsen under “business as usual”, doesn’t depend solely on human temperature records. We also have observations of radiation imbalance, studies on climate sensitivity, the physics of the greenhouse effect, observed ocean warming that fits with the amplified greenhouse effect, independent proxy datasets, and other evidence for ongoing change in the averages, in the absence of an associated natural forcing.

7. “Isn’t ‘black carbon’ from developing nations the problem?”

Black carbon (AKA soot) is viewed as a secondary contributor to climate changes, with significant regional effects. The melting of some glaciers may be attributed in part to soot, from things like dirty coal-fired power plants, unregulated diesel engines, and developing nation stoves. Soot is an easy target that could be relatively cheap to address, and with more immediate effect, but research is ongoing as to the likely net result of such targeted efforts. To some, this represents an opportunity to shift attention from CO2 (even briefly), despite it being a much larger long-term threat that will take more work to mitigate. It’s worth noting, though, that CO2 reduction and soot reduction can to some degree go hand-in-hand.

8. “What about claims of impending cooling/ice age aversion?”

Robert W. Felix, a former architect, received some publicity for his book and website claiming that we’re actually entering an ice age, and that glaciers are growing (more below). These claims were repeated by botanist David Bellamy, and posted on “skeptic” sites like Steve Milloy’s “” (more). The assertions were traced to figures published by Fred Singer (who, like Milloy, was connected with TASSC, and also with dubious petition projects, below). Singer stated his source as “A paper published in ‘Science’ in 1989” – nowhere to be found. This and other papers (most outside of peer-reviewed climate journals) suggesting we’re entering a long-term cooling phase have been roundly discredited.It has also been suggested that we’re averting another ice age by tipping the climate scale with greenhouse gas emissions. Although we’ve probably already tipped that scale enough to significantly delay a Milankovitch-type glaciation, indications are that Earth is nowhere near due for another glacial period anyway. Humanity has been blessed with one of the longer interglacials. Still, there are those who have used the ice age aversion argument as positive spin. They’re essentially implying that rapid holocene warming is fine because we’ll avert the subtle multi-millennial cooling (or very rare, ‘well-timed’ supervolcanic eruption) leading to the next big freeze. But if we’re still around, we can consider measured greenhouse gas emission/other geo-engineering to avoid glaciation. For now, humans are in a period of development that may eventually make us less vulnerable to disaster. It’s in our interest to value and prolong the time we have.On a related issue, there’s a common myth that climatologists predicted an imminent ice age in the 1970’s, despite the infancy of the science & technology, and acknowledged uncertainty on the future trajectory of climate forcings. While there was some speculation (along with caveats) and some overzealous media coverage, there’s more to the story than today’s naysayers admit. Update: A more recent review paper affirms what the scientific literature was actually saying.

9. “Natural processes will fix the imbalance”

This is essentially true, but it leaves out two important factors: The timescales involved and the damage done in the meantime. Once the source diminishes, an imbalance tends to self-correct, but not necessarily in a quick and convenient manner. During the paleocene-eocene thermal maximum, carbon accumulation occurred over 10,000 years, and recovery took about 100,000. At this point, things are a bit different, but not in a way that allows us to continue as usual. In fact, evidence suggests humans are releasing carbon at a much higher rate than the natural emissions leading into the PETM (which appears to have occurred with less than a doubling of carbon), and that climate change in today’s less warm-adjusted world has the potential to occur faster. If this compromises Earth’s carbon sinks, a multi-millennial recovery wouldn’t be out of the question.

10. “Won’t life just adapt?”

Rapid warming is a multi-faceted problem, with ecosystem impacts being one result. Some organisms may readily adapt (many of them at the expense of their populations), while others can’t simply adjust in a matter of decades or centuries. Thousands of species, including some that play vital roles in complex ecosystems, are at risk (see link section). More discussion here.

11. “What about religious views of global warming?”

For those with a Bible-based perspective, the question becomes whether there’s direct divine control over Earth’s life-supporting systems (thus we can freely trash them), or whether a sustained quasi-equilibrium has been set up that allows our actions (born out of free will) to demonstrate either stewardship or disregard. And which seems more responsible: To assume the former because it’s easy and convenient, or the latter because it’s not worth gambling with the future (a future that could be millennia, despite ever-present predictions of apocalypse)? Several religious groups have decided it’s better to err on the side of caution and accept some responsibility for the environment that sustains us. Others selectively interpret the Bible as supporting careless plunder, while disregarding passages that suggest such things as humanity’s self-determination.

12. “More solar activity is responsible, and Mars/Pluto prove it.

Some highlight the sun as the primary cause of global warming (often selectively citing snippets from Solanki et al. 2004), but the science doesn’t support this. Although the sun goes through 11-year activity cycles, and contributed to moderate (but regionally significant) warming in the early 20th century, it doesn’t account for the strong trend of recent decades. A 2006 NCAR study (Foukal et al.) affirmed with satellite and proxy data that solar flux has made a negligible contribution to accelerated warming over at least the past 30 years, and that luminosity changes had a moderate influence over the past thousand years or more. Lockwood & Frolich note in another study that “over the past 20 years, all the trends in the Sun that could have had an influence on the Earth’s climate have been in the opposite direction to that required to explain the observed rise in global mean temperatures”. Other solar-related claims have also taken it on the chin (Update: Second study casts doubt on cosmic ray influence on the global trend, and yet another paper indicates only a modest solar influence on 20th century warming). Additionally, the stratosphere has been cooling (#24), consistent with an amplified greenhouse effect but not with a significant increase in average solar output.


The latest standing scientific papers agree that the sun isn’t driving the ongoing trend (more here). A trend that has remained robust despite a quiet sun in recent years, as well as the temporary offsetting effect of natural and manmade sulfates, and cyclically greater ocean heat retention at depth.In any case, elevated levels of greenhouse gas trap additional solar energy whatever it’s intensity. The fact that the greenhouse effect strongly influences Earth’s climate makes it an important part of the equation. If it were allowed to snowball, and a period of substantial solar warming were to occur in the future, one has to wonder about the results.Re: Mars and other planets – Even if there were a global warming trend on Mars (vs. a changed polar ice cap over a few Martian seasons), there are no oceans there, much of the ice isn’t composed of water, and the atmosphere is much thinner. So temperatures are bound to be more sensitive to even small solar changes. But as noted by astrophysicist Steinn Sigurdsson, there are other factors at work on Mars unrelated to the sun’s output (which, overall, had been declining slightly as it moved towards solar minimum). The much greater influence of orbital eccentricity, strong seasonal variation, and the strength & duration of hemispheric dust storms are also involved. And of course that’s a change on of Mars over several years, vs. a trend over decades on Earth. For Pluto, warming has been inferred from a change in atmospheric thickness over less than one Plutonian season, following a close approach to the sun. Other bodies in the solar system also have very long seasons and orbital periods (even centuries), or surface conditions driven mostly by internal energy sources, so they can’t be used as solar indicators either.More here on the climates of other planets.

13. “The CO2 increase is natural”/”Ocean warming is responsible for the rise in CO2.”

The question is, what’s causing that ocean warming if solar activity can’t account for most of it? A few “skeptics” have suggested undersea volcanoes, but a major activity increase (for which there’s no evidence) would be required to globally heat the oceans a fraction of a degree, and they’re also warming from the surface down. Earth’s average geothermal heat flow is negligible compared to the energy received from the sun or retained by the greenhouse effect. A recent Scripps study (see sidebar) affirms that patterns of oceanic warming are consistent with CO2 forcing (as are other changes). And in terms of CO2 exchange, the oceans still represent an absorption of about 2 GtC (subject to decline as temperatures rise and ocean chemistry changes). Even fossil fuel accounting, and the fact that part of our carbon output doesn’t remain in the atmosphere, indicates that nature remains (at least for now), a net carbon sink, not a source. Scientists can also measure how much CO2 is from fossil fuels:How do we know that recent CO² increases are due to human activities?

14. “But ice core data shows that warming boosts CO2, not vice versa.”

This claim not only ignores the traceable origins of the current accumulation (above), but it leaves out some important details. During glacial period terminations, recovery of atmospheric CO2 acted as a feedback to amplify warming triggered by Milankovitch orbital forcing. This doesn’t mean CO2 can’t itself be a significant climate forcing (a cause of change rather than just a response). It just never has (until now) over the entire 800,000 year ice core record. More from Realclimate.Jeff Severinghaus, Professor of Geosciences at Scripps notes:  “All that the lag shows is that CO² did not cause the first 800 years of warming, out of the 5000 year trend. The other 4200 years of warming could in fact have been caused by CO², as far as we can tell from this ice core data”.According to Caillon et al, 2003, “the CO² increase clearly precedes the Northern Hemisphere deglaciation”…And referring again to our 650 kiloyear CO2 chart, we can see the other difference between then and now:

CO2 650 Kiloyear

15. “Aren’t the oceans actually cooling?”

A study by Lyman et al showed a decrease in oceanic heat content from 2003-2005. Such variability wouldn’t necessarily indicate a new trend.  But there also seems to be an inconsistency in this study: Sea level should have dropped along with temperature, unless there’s been a sharp increase in ice melt. Ocean circulation changes and variability in heat exchange with the deeper ocean are variability factors. While the study is still under review, short-term inconsistency in warming wouldn’t be surprising.Update: Peer review at work. Lyman study seems to have a data problem, cooling has disappeared in latest analysis. And some discussion here and here of trends and updates since.

16. “What about methane?”

Although it’s emissions and concentrations are much lower than those of CO2, methane is a more powerful greenhouse gas, and has the potential to play a significant role in future warming. Along with the again rising levels of directly human-induced emission, feedbacks are likely to release more methane as warming progresses. One scenario, modeled by an NCAR supercomputer, involves warmer water releasing methane currently frozen under the sea floor (see sidebar). Thawing permafrost, though, may have more feedback potential over the next several decades.

17. “Volcanic/other natural emissions far exceed those of humans.”

CO2 out-gassing from volcanism may have been a significant climatic influence in prehistory, but more “recently” in geologic time, it has been dwarfed by human output (currently about 30 gigatons total mass/8 gigatons carbon equivalent). NASA’s Gavin Schmidt notes that there are both direct volcanic emission measurements (see here), “… and also isotopic and mass balance arguments that absolutely, 100%, no question about it, mean that the current rise in CO2 is anthropogenic”. Even supervolcanic eruptions in prehistory have had much less impact on atmospheric concentrations than the sustained human output.


Another volcanic gas, sulfur dioxide (SO²), can have a temporary cooling effect.But the real issue is a significant change in CO2 concentration. Overall, natural CO² emissions have been balanced by absorption. A simplified example: The trees that burn in a forest fire contain carbon that was previously removed from the atmosphere. As the forest regenerates, CO² is re-absorbed. With continued warming, though, wildfires are expected to become more frequent and severe, further disrupting the carbon cycle. Update: Rise in wildfires linked to climate change.

18. “CO2 trend data from Mauna Loa is biased by the volcano”

Readings are taken upwind from volcanic vents, out-gassing is monitored, and any short-term spikes are flagged for removal, but even if the Mauna Loa figures were tainted, the volcano can’t explain a long-term upward trend. There are also multiple isolated measurements around the world, including in Antarctica, that agree well. More here on the choice of Mauna Loa, and here on measurement reliability/verification.

19. “Is deforestation affecting climate?”

While fossil fuel combustion is the primary factor, deforestation results in the release of about 1.6 gigatons of carbon annually. The impact is highest in the tropics, in part because those forests (which tend to be ecologically sensitive) are often burned for pasture, and changes may be essentially permanent. Forest loss can reduce the land-based carbon sink, and re-forestation can help offset carbon cycle impacts, but net absorption rates are influenced by multiple factors, including forest type and regional climate. Although tropical forests are often called the “lungs of the Earth” (and they are large carbon reservoirs), they are in fact less of a sink than the world’s oceans.

20. “Extra CO2 will be beneficial/Plant growth will correct the imbalance.”

It has been argued by certain fossil fuel interests that higher CO² levels will enhance plant growth and benefit agriculture. This is true to a point, under the right conditions. But in the real world, plant growth and productivity are more limited by factors other than CO2 concentration (which is already quite sufficient to support healthy growth rates). Growing conditions are likely to change (insect populations, water availability, extreme weather events…), and a comprehensive Stanford University study found that elevated CO² only stimulated growth when nitrogen, water and temperature were at normal levels. It was also suggested that excess soil carbon or initially accelerated growth may limit the availability of nutrients. Some “weedy” plants may benefit disproportionately from extra CO2, but they would need to somehow overcome present-day geographic limitations and more than triple the net terrestrial carbon sink to counter most of our current emissions. Any enhancement of a sink helps, but the accumulation already in progress is exceeding sequestration by plants, and oceanic dissolution. For more detail on considerations in agriculture, see the consequences page.

21. “What about the role of clouds and precipitation?”

Some contrarians have suggested that extra cloud cover might offset warming. John Christy of UAH speculated on this, and also stated (to digress for a moment) that “Whatever happens, we’ll adapt”. The question is how many of Earth’s billions of people (ecology aside) might adapt, at what cost, and with what quality of life? Regarding clouds, though: Although storm intensity may increase, rising temperatures also mean more water can remain uncondensed in the troposphere. The likelihood of significant cooling from thick, low-level cloud cover appears questionable. Additionally, proponents of the cloud-cooling theory don’t seem to indicate why negative feedback had trouble keeping up with the last carbon accumulation event in prehistory, or even how Earth has come out of glacial periods despite a supposedly strong negative feedback. Betting on altered cloud cover is probably unwise.Depending on their type, clouds can on balance reflect energy from Earth or trap it in the atmosphere. They can reduce daytime warmth, but also keep overnight temperatures higher and provide a head-start for daytime heating. An overall increase in winter lower-level cloud cover and a reduction in the summer would have a warming influence. The net effect is an area of intensive study. All climate models project significant warming, but cloud behavior may help determine whether it will be closer to the high end or the low end of the range. Update: New research suggests the higher end.Spencer & Christy, previously known for promoting a flawed satellite temperature record,  released a paper suggesting that an inter-annual cooling effect in the tropics may have implications for the projection of global warming. See How to cook a graph in three easy lessons.

22. “What about ‘aerosols’, contrails, and ‘global dimming’?”

Global dimming refers to a reduction of solar energy at Earth’s surface caused by particulate/”aerosol” pollution and it’s interaction with clouds. Aircraft contrails also have a small (on average) effect, but this ends up as a slight warming from infrared re-radiation. The cooling effect of aerosols has partially masked global warming and presents what seems like a pollution control conundrum. In the 1990’s, this effect showed signs of declining, making CO2 emission reduction that much more important. Currently, particulates and sulfur dioxide (source of sulfate aerosol) are reduced for the sake of cleaner air. CO2 output often goes unchecked.

Another effect of these pollutants seems to be the intensification of winter storms in the northern Pacific (and disruption of vital Asian monsoons), and their circulation of warmer air to the Arctic (Zhang et al, 2007). In other words, such pollution may worsen warming-induced changes in some regions.

23. “Don’t El Niño and La niña influence climate?”

These are an oscillation related to the circulation of tropical Pacific heat. The global average temperature impact of a strong El Niño is about 0.2 degrees C. Although a significant natural influence on weather patterns and contributor to inter-annual fluctuation (see graph at the top of this page), the temperature effects of the natural cycle smooth out over years, and aren’t a cause of the overall trend. However, the effects of El Niño may be “enhanced” by global warming, since the oscillation essentially pools oceanic heat and alters moisture flow. Recent NASA and NOAA research suggests that much of the increase in Pacific sea surface temperatures in recent decades has so far manifested itself in the form of stronger central Pacific El Niños, but macro-level circulation patterns like the Interdecadal Pacific Oscillation influence which decades are more dominated by El Niño vs. La Niña. Discussions of how the average magnitude and persistence of El Nino may be affected here and here.Related:
Natural ENSO responsible for warming trend?
“Atrocious” paper makes it into JGR

24. “What about ozone, stratospheric cooling, and CO2 band saturation?”

Although sometimes confused in the media, stratospheric ozone depletion and global warming are largely separate concerns. The main problem with ozone depletion is higher levels of damaging ultraviolet radiation. This is already being successfully tackled (see here for more, including footnotes) with an international phase-out of ChloroFluoroCarbons, while global warming needs to be addressed via reduced emission of greenhouse gases (“GHGs”) like carbon dioxide. The two issues, though, are somewhat interconnected.CFCs (and some of their substitutes) and tropospheric ozone are also greenhouse gases (relatively minor ones compared to CO2). And, as counter-intuitive as it may seem, the amplified greenhouse effect causes stratospheric cooling (simplifying, more GHG in the troposphere reduces infrared re-radiation to the stratosphere). Ozone depletion itself contributes modestly to such cooling.The claim that band saturation severely limits CO2 as a climate forcing is a myth (more here and here, and this on the claims of Ferenc Miscolczi), derived from a concept widely considered flawed since the 1950’s. The upper atmosphere and the “wings” of the CO2 absorption band are rather important, and models already represent CO2 forcing as the natural log of it’s change in concentration (leaving plenty of climate-shifting potential).

25. “Aren’t glaciers growing?/Isn’t Antarctica cooling/Sea ice growing”

These are popular half-truths that mislead. Partly due to heat uptake by the southern ocean and lower surface melt, ice sheets in East Antarctica have remained relatively stable (consistent with model projections), and appear to have received some extra snowfall. Some snowpack thickening has also been observed in Greenland at high elevations. This is related to the regional precipitation of extra moisture, and is not inconsistent with a warming world. Despite this, and a slight cooling in parts of Antarctica, most of the world’s glaciers have been receding as part of an inter-decadal trend, and ice loss has accelerated in Greenland (resulting in a large net mass reduction).

Hansen figure 7

Above is one example of feedback: A moulin (vertical shaft) carries meltwater to the ice sheet base, where it can (depending on sub-glacial characteristics) act as a movement-accelerating lubricant.

On Antarctica, new research shows a significant net loss of land ice (while the growth of Antarctic sea ice has been attributed to a complex interaction of strengthened cyclonic winds, and changes in precipitation and ocean circulation).

For Arctic sea ice, there has been a clear multi-decadal decrease in annual minimum extent and volume.

Update: Antarctic Loss Speeds Up, Nearly Matches Greenland. Update2: Ice sheet-ocean margins more vulnerable, important than realized.

Antarctic Ice MassArctic sea ice volumeArctic Real-time updated sea ice volume shows recent uptick but not a trend reversal:Sea Ice Volume

26. “Is there a link between warming and hurricanes?”

The connection between recent hurricane strength and early-stage global warming has been an area of some debate. The link with hurricane frequency is even more so. It’s typically difficult to prove a direct causal link with a particular event, since such events are a confluence of regional dynamics and the overall trends related to Earth’s energy balance. Ocean warming simply makes more energy and moisture available for potential concentration, thereby increasing the odds of a severe event. Research (such as Emanuel, Knutson, Webster et al.) indicates an intensity trend influenced by warming. As warmer temperatures spread north, tropical cyclones can also stay intact longer.Even a seemingly small rise in sea surface temperature means extra water vapor and energy for a storm to pick up (while el niño or Saharan air layer conditions can periodically suppress hurricanes in the Atlantic). There is also the element of rising sea levels and their contribution to storm surge. Although the IPCC estimates are often cited, those carried substantial caveats regarding dynamic ice sheet disintegration, and the lack of thoroughly reviewed projections for it as of the AR4. More recent research suggests we could see a foot of sea level rise (on average) by 2050 and 4-6 feet by 2100. And some of the newest, preliminary research is exploring the possibility that high pressure blocking ridges in a warming Arctic can influence the path of a storm like Sandy, so it’s less likely to drift out to sea.Still, certain TV meteorologists and media outlets have quickly dismissed any climate change connection, ignoring the ongoing scientific inquiry, often focusing on frequency rather than intensity, and chalking everything up to a natural Atlantic cycle (controversy followed). The research, though, found an intensity trend in Pacific and Indian ocean storms as well. This earlier article addresses the issue further.


New Research Shows Humans Causing More Strong Hurricanes

Gray and Muddy Thinking about Global Warming
A look at William Gray’s contrarian arguments

Clarity Emerging on Hurricanes?

Skeptical Science: What is the link between hurricanes and global warming?

27. “Is there some level of consensus among climatologists?”

Although consensus isn’t the point of science, and some might mock it, there have been relatively few cases of established scientific tenets being fundamentally overturned in modern Earth science. For every Galileo-type challenge that succeeds in establishing an alternative theory, there are many others that fail. In climatology, the peer-reviewed literature and periodic assessments, and major scientific organizations indicate wide agreement on several main points, including that there’s a significant human influence on climate:

Skeptical Science on the consensus

The Wall Street Journal vs. The Scientific Consensus

28. “Climatologists exaggerate/perpetuate the concept of human influence for funding.”

As Ray Pierrehumbert put it: “Money and perks! Hahahaha. How in the world did I miss out on those when I was a lead author for the Third Assessment report? Working on IPCC is a major drain on ones’ time, and probably detracts from getting out papers that would help to get grants (not that we make money off of grants either, since those of us at national labs and universities are not paid salary out of grants for the most part). We do it because it’s work that has to be done. It’s grueling and demanding, and not that much fun, and I can assure everybody that there is no remuneration involved…” And “…scientists are probing theories and conceptions all the time, trying to break them. The best way to become famous is to overturn established wisdom, so scientists look hard all the time for opportunities to do this.”Further, much attention is applied to areas of uncertainty – something climatologists concerned mainly about money would over-emphasize, rather than affirming the primary role of human activity. We also have the reality that many climate researchers are tenured/conduct research as they see fit, and that funding goes into cutting edge research and expensive equipment. Can the same be said of funds disbursed to contrarians by the fossil fuel industry? Even the finding of a significant natural factor would attract research grants. And there have been decades of opportunity for any number of skeptical scientists to overturn the case for anthropogenic influence. Instead it has grown stronger.

29. “So what can be done?”

Climate change and our energy situation are big problems that require a combination of solutions across multiple sectors. We need to start now rather than simply betting on technologies that may not be viable in time to avoid locking in dangerous effects. Dr. Romm lays out one reasonable plan here, while discussing the “breakthrough technology illusion” here. Alternative energy sources that result in little or no net CO2 emission (from production or consumption) will play a role, but there must be a focus on reducing waste/improving fuel efficiency as well. The best way to spur such changes, and recognize the externalized costs of fossil fuels, may be through a cap & trade system that reduces their persistent cost advantage, and provides rebates or incentives to consumers. Similar systems have been supported in the past by even Republican administrations to phase lead out of gasoline and moderate sulfur emissions (see sidebar). If that isn’t doable on the scale necessary to cut carbon output, we at least need a concerted effort to redirect fossil fuel subsidies (direct and indirect) to efficiency and alternative energy. In any case, the longer society waits to quicken the transition, the more difficult and expensive the future is likely to be.

For some basic things we can do now to address the issue of global climate change, see sidebar.

30. “Is ‘clean coal’ an option?”

Newer coal technologies have the potential to reduce CO2 emission, but significant cuts will only be made by gasification plants that implement carbon capture and storage/sequestration (CCS). IGCC plants can make separation economical, but the CO2 must then be compressed, transported, and sequestered. Except where it can be sold for enhancing oil extraction, this represents an expense unlikely to be widely accepted without ongoing subsidy and/or CO2 regulation. This and other problems with the technology (here) make large scale deployment unlikely in the foreseeable future. As of this writing, there are no commercial CCS operations planned, but this doesn’t stop coal interests from advertising the technology as if it were right around the corner. Additionally, “coal to liquid” fuels represent a double CO2 pollution load unless CCS is employed. Even then, there would be no difference between the impact of coal fuels and petroleum fuels.

31. “Improving efficiency and cutting emissions will ruin our economy.”

Fossil-funded political organizations have released reports on the costs of acting that provide little detail and ignore or underestimate the benefits. Further delay is more likely to ruin our economy, both in terms of the lasting effects of climate change, and rising fuel prices as demand outpaces cheap extraction. Higher prices may be good for oil companies with the most robust reserves, but they will impact everything produced and/or transported with oil, including plastics, building materials, and even food (think agricultural chemicals and diesel). The costs of climate change alone are likely to be very steep compared to the costs of acting to limit global warming. Economic implications and claims of economic ruin are further discussed here (including the relevant link at the end) and here.

32. “But doesn’t mean consumption/’cow emission’ have more impact than fossil fuels?”

This might seem like an odd one, but a 2006 UN report suggested that livestock production results in (modestly) more greenhouse gas emission, in CO2 equivalent, than the transportation sector. The 18% figure includes methane (6%) and nitrous oxide (3%) output, and also CO2 from forest burning & fossil fuel inputs (9%). Nitrous oxide forcing has been growing moderately (recently 0.16 W/m2 vs. 1.66 for CO2) and methane is so far lingering around 0.5 W/m2.

Another study suggested that up to 51% of human greenhouse gas forcing can be attributed, directly or indirectly, to animal agriculture, but controversy abounds given the difficulty of what they authors attempted to do: Count respiration emissions that are typically considered carbon-neutral. The jury is still out on the robustness of the numbers, but suffice it to say that modern cattle production is a significant contributor, and moderating meat consumption could be a larger part of mitigating accelerated climate change. Meanwhile, though, CO2 emission from transit and power generation continues to grow rapidly, and may take more time to mitigate (since associated supply systems are decade-scale investments). Therefore, it’s important to address all significant sources, agricultural and otherwise.

33. “Aren’t automakers improving efficiency/developing alternatives?”

Following the improvements of past decades spurred by clean air regulation, most manufacturers resisted applying efficiency technologies in a significant way, releasing limited lines of enhanced vehicles (including flex fuel that can take advantage of the modest net benefit of ethanol), and then developed ad campaigns appealing to concerns about fuel prices. Recent increases in fuel economy standards should finally spur some real change, and may eventually produce a moderate sustained emissions reduction. That is, assuming that potential loopholes in the law don’t result in lower than advertised increases.

For vehicles that burn ethanol, availability remains an issue in many regions, and without further efficiency improvements (in both production and combustion) the net benefit is very limited. As production methods advance and agricultural wastes are utilized, ethanol could be a valuable supplement, since the plants used to produce it are part of the present-day carbon cycle (they absorb atmospheric CO2 in order to produce the carbohydrates the fuel is derived from). But the liquid transportation fuels with the most promise for having a small carbon footprint (cellulosic ethanol, biobutanol, and algal biodiesel) are not currently scalable or commercially viable, and at present consumption levels they may have a hard time gaining a foothold. This makes conservation more important than ever.

There’s also been a lot of hype over hydrogen as a fuel. Although it may have potential as the energy situation improves, widespread use would be decades away at best. The key issues are the lack of necessary infrastructure, the low energy density of hydrogen compared with hydrocarbons, and the fact that hydrogen isn’t an energy source. It must be generated from water or fossil fuels, and takes more energy to produce, store, and distribute than it yields in combustion. Fuel cells may eventually offer enough output and overall efficiency at reasonable pre-subsidy cost, but probably not anytime soon. Hydrogen hype may be beneficial to oil & gas companies likely to build infrastructure and provide potential fossil feedstocks, and it may leave the impression that they’re making an effort to ease our petro-addiction. In reality, focusing on hydrogen could delay the transition from fossil fuels, and require additional energy supply and higher efficiency to satisfy demand.

34. “What about China?”

It’s a common argument, often used to deflect responsibility, that China is surpassing the U.S. in CO2 emission, but isn’t required to improve (therefore, the U.S. shouldn’t bother). First, China is now investing more than the U.S. in energy solutions (although they also have a bigger challenge to tackle). Second, the West has been emitting large amounts of CO2 longer, and still easily outpaces China in per-capita emission. There are over a billion people in China, yet their total output is nearly the same as ours. The fact that there are still heavy growth pressures in China makes it less likely that they’ll adopt a nationwide carbon tax before seeing some real commitments from the West.

Some argue that efficiency (at least industrial efficiency) is higher in the U.S./CO2 emission is lower per unit of GDP. Differences in purchasing power aside, the U.S. has also shifted much of it’s energy intensive manufacturing overseas and become more of a “service economy”. As a result, we’re indirectly responsible for part of China’s carbon footprint. We’re all in this together. Most countries can do better, but the U.S. is in a position to help foster technologies globally.

35. “Hasn’t the climate been cooling for years?”

This is an oldie that began with people like Pat Michaels (#2 above) and Geologist & prolific contrarian Bob Carter (here, here, and here). This claim takes advantage of annual to decadal fluctuation in atmospheric temperatures, and is made by selecting a short, exceptionally warm period as a basis for comparison. For example, the strongest el niño of the 20th century helped make 1998 a record year in the CRU surface dataset, with 2005 being a close second (the NASA and NOAA data, which unlike CRU represents the fast-warming Arctic, pegs 2005 and 2010 as the warmest years on record). So choosing 1998 as a starting point is a classic cherry pick. Since climate change is based on trends of greater than a decade, relative to a long-term average, it’s invalid to make claims based on individual years.

Even with later years (particularly those affected by la niña) being a bit cooler, the averages remain anomalous in the longer-term context, and 9 out of the ten warmest years on record all occurred in the past decade. And because the exchange of heat between the oceans and the atmosphere can vary, some modest near-term cooling of the atmosphere wouldn’t necessarily mean Earth is actually losing more heat. See here for more.

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