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!”
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:
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’?”
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?”
9. “Natural processes will fix the imbalance”
10. “Won’t life just adapt?”
11. “What about religious views of global warming?”
12. “More solar activity is responsible, and Mars/Pluto prove it.
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.”
14. “But ice core data shows that warming boosts CO2, not vice versa.”
15. “Aren’t the oceans actually cooling?”
16. “What about methane?”
17. “Volcanic/other natural emissions far exceed those of humans.”
18. “CO2 trend data from Mauna Loa is biased by the volcano”
19. “Is deforestation affecting climate?”
20. “Extra CO2 will be beneficial/Plant growth will correct the imbalance.”
21. “What about the role of clouds and precipitation?”
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?”
Natural ENSO responsible for warming trend?
“Atrocious” paper makes it into JGR
24. “What about ozone, stratospheric cooling, and CO2 band saturation?”
25. “Aren’t glaciers growing?/Isn’t Antarctica cooling/Sea ice growing”
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.
26. “Is there a link between warming and hurricanes?”
Gray and Muddy Thinking about Global Warming
A look at William Gray’s contrarian arguments
27. “Is there some level of consensus among climatologists?”
28. “Climatologists exaggerate/perpetuate the concept of human influence for funding.”
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.