Debunking Urban Legends
Legend 1: Solar Variations
Climate change is happening but is caused by solar variations beyond human control.
Frances Moore, Research Associate, The Climate InstituteApril 24, 2007The most apparent variations in solar intensity are linked to the 11-year sunspot cycle. Satellite observations indicate that solar intensity only varies by around 0.1% or about 0.24 W/m² over one cycle. As a result, the timing and amount of change in solar radiation are unable to account for the large and steady increase in temperature since 1970.
It has also been hypothesized that the sun varies on longer timescales than the 11-year sunspot cycle. However, reconstructions of the long-term variations in solar activity over the last 400 years are only able to explain a small fraction of the warming observed in the industrial period.
Figure 1. This diagram shows how the modeled effects of natural phenomena such as variations in solar intensity or volcanic emissions (shown by the blue band — a mean of multiple model simulations) are unable to explain the steady rise in temperature over the last forty years (shown by the black curve). Adding in the effects of anthropogenic emissions of greenhouse gases and aerosols to the models (red band) provides a very good reproduction of the observed temperature changes over the 20th century. (Meehl et al., 2004).
The cooling of the stratosphere (the part of the atmosphere between 10 and 20 km from the surface) that has accompanied the recent warming of the surface is a 'fingerprint' of the effects of an increase in greenhouse gas concentrations. If warming were caused by an increase in solar radiation, warming of both the stratosphere as well as the lower atmosphere and surface would be expected, which is not what has been observed.
Legend 2: Plants Emission
Plants emit more carbon dioxide than humans, so why aren't we blaming them?
By Frances Moore, Research Associate, The Climate InstituteApril 24, 2007
It's true that the trees, plants, and animals (collectively called the biosphere) emit about ten times more CO2 every year than humans. This happens through respiration when biomass is converted into carbon dioxide and water, releasing the energy that powers life in the process. However, all that CO2 is taken up by plants when they create biomass during photosynthesis, leaving no net change in the atmosphere.
There tends to be a strong seasonal signal to this process because a lot of respiration happens during the fall when leaves fall off trees and decay, releasing CO2 into the atmosphere. But again, all that CO2 is taken back up by forests when the leaves re-grow in the spring, again leaving no net change in the atmosphere.
What is really relevant to climate change is the net emissions of CO2 (sources minus sinks) over an extended period. In equilibrium, all natural sources of CO2 will be balanced by natural sinks that remove CO2, meaning they do not increase the amount of CO2 in the atmosphere. Anthropogenic emissions from fossil fuel combustion are not completely balanced by a sink and so represent a net source of CO2 to the atmosphere that increases greenhouse gas concentration and warms the planet.
Legend 3: CO2 Cause-Effect
Ice-core records show that increases in temperature precede increases in atmospheric CO2 during inter-glacials (the time between ice ages), so changing CO2 concentration doesn't affect temperature, rather temperature affects CO2.
By Frances Moore, Research Associate, The Climate InstituteApril 24, 2007
Paleoclimatic records such as ice cores and ocean sediments indicate that the cycling of ice ages over the past several million years has been controlled by changes in the intensity of sunlight in the Northern Hemisphere summer due to variations over tens of thousands of years in the orbit of the Earth around the sun (the so-called Milankovitch cycles).
Positive feedback mechanisms related to the release of greenhouse gasses such as CO2 and methane amplify the effect of the orbital cycles and lead to large changes in Earth's climate. CO2 increased during interglacials because a warmer ocean doesn't hold as much carbon dioxide as a cold ocean and so oceans released some back into the atmosphere as the planet warmed. This increase in atmospheric CO2 then further warmed the planet leading to the release of even more carbon dioxide. Given this understanding of the ice ages, we would expect increases in greenhouse gasses to lag increases in temperature at the end of a glacial period, which is just what we see in the geologic record.
Just because carbon dioxide was not the factor driving climate change during the ice ages, does not mean that it is not today. Anthropogenic emissions of greenhouse gases are initiating the cycle of warming through a different mechanism then what happened previously during inter-glacials, but the warming effect of CO2 is the same in both cases.
There is also plenty of evidence in the longer geological record that greenhouse gases have had a major influence on planetary temperature in the past. Examples are the Palecoene-Eocene boundary (55 million years ago) and the late Cretaceous (around 80 million years ago).
Legend 4: Natural Variability
Global warming is all part of natural variability; the climate is always changing.
By Frances Moore, Research Associate, The Climate InstituteApril 24, 2007
The only way to assess whether the recently observed warming fits with a pattern of natural variability is to look at how temperature has varied in the past. This can be done using paleoclimatic evidence from tree rings, glaciers, corals, and other geologic records. Figure 2 shows several different reconstructions of temperature for the past two thousand years with the instrumental record shown in black. It is clear that the magnitude and rate of change over the past century far exceeds any natural variation that occurred in the past two millennia.
While there have been large variations in climate over the course of Earth history, paleoclimatic evidence can often tie these to specific changes in climate forcings, such as variations in Earth orbit or changes in atmospheric composition. Once variations resulting from known external forcings are removed, the magnitude of natural fluctuations from the chaotic variability inherent to the climate system appears to be significantly smaller than changes in global average temperature over the past century, suggesting that this change is a response to forcing from increased greenhouse gas concentrations caused by humans rather than a simple internal oscillation.
Figure 2. Several temperature reconstructions for the past two thousand years using various paleoclimatic proxies, with the instrumental record shown in black. Older reconstructions are shown in blue and those published more recently are shown in yellow or red. Image from the Global Warming Art Project.
Legend 5: Can't be CO2
CO2 makes up a tiny fraction of the atmosphere so how can it be important?
By Frances Moore, Research Associate, The Climate InstituteApril 24, 2007
The climatic influence of a given atmospheric gas depends both on its concentration in the atmosphere and its effectiveness at absorbing outgoing radiation. For example, although nitrogen makes up about 80% of our atmosphere, it can not absorb visible or infrared radiation and so has no effect on climate. In contrast, the molecular structures of greenhouse gases make them effective absorbers of outgoing infrared radiation so even a small amount can have a large influence over the climate.
We know that even the relatively small concentrations of greenhouse gases in our atmosphere at the moment have a large effect on climate because without them, given our distance from the sun, our planet would be about 30#C cooler than it actually is - cold enough to freeze the oceans. The warming caused by greenhouse gases is what allows liquid water to exist, which in turn is essential for supporting life on our planet.
Legend 6: Blame Water Vapor
Water vapor accounts for more greenhouse warming than carbon dioxide, so that must be causing climate change.
By Frances Moore, Research Associate, The Climate InstituteApril 24, 2007Water vapor is indeed the most abundant greenhouse gas, but its concentration is closely controlled by the temperature of the atmosphere and oceans with little influence from external forcing mechanisms. In other words, water vapor tends to act as an amplifier of an existing warming trend, rather than as a driver of changes in climate. The warming caused by increases in the concentration of CO2 and other greenhouse gases has allowed more water vapor to be held in the atmosphere (since warmer air can hold more water) which in turn causes further warming. In this way, water vapor acts as an important positive feedback mechanism, but is not the primary driver of climate change.
Legend 7: Data Inaccurate
Satellite temperature data of warming in the mid- to low-troposphere (0 to 10 km above the surface) does not support global warming.
By Frances Moore, Research Associate, The Climate InstituteApril 24, 2007
This claim is based on very early, and now outdated, versions of the satellite estimates of tropospheric temperature. Satellites can not directly measure atmospheric temperature but instead measure atmospheric radiance from which temperature can be derived using complicated models and calculations. This process ultimately gives estimates for the temperature change only of thick layers of the atmosphere. feedback mechanism, but is not the primary driver of climate change.
While early data sets showed little or no tropospheric warming, problems were later found in how the data had been processed, in the calibration of instruments from one satellite to the next, and in the observations from weather balloons that were used to calibrate the satellite estimates of temperature change. Correcting these problems yields results that greatly reduce the apparent inconsistency between warming in the troposphere and on the surface and shows that the troposphere has warmed significantly. Continuing study is underway on remaining difference between surface and tropospheric data sets. This report from the U.S. Climate Change Science Program has more information.
Figure 3. The colored marks show model predictions of temperature change at the surface and troposphere (the part of the atmosphere below 10km) over 1979-1999. The black square represents the most recent analysis of satellite data, which shows that the troposphere has warmed significantly in recent decades and now corresponds (within error limits) with model predictions. (Santer et al., 2005).
Legend 8: Warming is Good
Climate change is happening but it will be good for us.
By Frances Moore, Research Associate, The Climate InstituteApril 24, 2007
In general, societies around the world have adapted to the present climate - growers know when to plant their crops, houses are built to be cool where it is hot and warm where it is cold. Because of the effort and resources devoted over time to this adaptation, changes to the climate will require adjustments to behavior and infrastructure that are likely to be very costly. (As a small example, over 180 villages in coastal Alaska will have to be relocated because of increased coastal erosion since the retreat of the sea ice. Each move will cost approximately $180 million.) Any benefits from climate change (and some, such as a longer growing season in Russia and Canada, do exist) are likely to be localized and insignificant compared to the more numerous negative impacts.
An important prediction of almost all climate models is that global warming will result in increasing weather variability. Such a change would be very likely to have only negative consequences because large swings in weather are damaging to crop production and human health, and make adaptation much more difficult.
Another very significant aspect of climate change, sea level rise, will only have negative effects because of the inundation of coastal land. A recent World Bank study estimated that a minimum of 57 million people would be affected by a sea level rise of 1 meter.
Crucial to this question is how fast changes to the climate occur. If changes were happening very slowly and gradually, it could be that adaptation would be less expensive and that positive effects would partly offset negative ones. However, changes over the next century are likely to happen very rapidly, making it difficult and expensive to take advantage of changes in a positive way. The recently released report from Working Group 2 of the IPCC details the best scientific estimates of the expected impacts from climate change, which include disruptions to ecosystems and the hydrological cycle, damage from increasingly severe extreme weather events, changes to patterns of infectious disease, and lower crop yields.
Legend 9: Warming Not Fair
Worrying about climate change is unfair to the developing world.
By Frances Moore, Research Associate, The Climate InstituteApril 24, 2007
This statement ignores the fact that the primary emphasis of the current climate change movement is on the reduction of emissions in developed countries. Because they are wealthier, and because their per capita emissions are so large, the onus is on developed countries to find new, carbon-free technologies that can be transferred to developing countries once they are well established.
The crux of the climate problem lies in the huge per-capita carbon footprint of the Western lifestyle, not in the provision of energy to the poorest people in developing nations. Were enough electricity and cooking fuel for basic human needs provided to everyone on the planet, global CO2 emissions would only increase by 3%. See the calculations by Robert Socolow here.
In fact, not worrying about climate change would be unfair to the developing world. Developing countries, which are the most vulnerable, stand to suffer the worst impacts from climate change and yet are least responsible for the problem because their emissions are so low. Lowering carbon emissions is crucial for ensuring that the imbalance between first and third world nations is not made worse as a result of climate change.
Many people in the developing world do not have access to electricity because importing traditional fossil fuels is expensive. Environmental and development NGOs are working to build cheaper renewable energy systems which have the win-win effect of increasing the availability of electricity and putting countries on a clean energy development pathway. An example is the Climate Institute's own Global Sustainable Energy Islands Initiative and the work that the Government of Iceland has been doing in promoting geothermal energy production from the Rift Valley in East Africa.
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