DB Climate Change Advisors
Climate Change: Addressing the Major Skeptic Arguments
September 8, 2010
Click here to download paper [PDF / 332.34 kB]
The purpose of this paper is to examine the many claims and counter-claims being made in the public debate about climate change science.
For most of this year, the volume of this debate has turned way up as the ‘skeptics’ launched a determined assault on the climate findings accepted by the overwhelming majority of the scientific community. Unfortunately, the increased noise has only made it harder for people to untangle the arguments and form their own opinions. This is problematic because the way the public’s views are shaped is critical to future political action on climate change.
For investors in particular, the implications are huge. While there are many arguments in favor of clean energy, water and sustainable agriculture – for instance, energy security, economic growth, and job opportunities – we at DBCCA have always said that the science is one essential foundation of the whole climate change investment thesis. Navigating the scientific debate is therefore vitally important for investors in this space.
For these reasons, we asked our advisors at the Columbia Climate Center at the Earth Institute, Columbia University, to examine as many as possible of the major skeptic claims in the light of the latest peer reviewed scientific literature and to weigh the arguments of each side in the balance. Although the scientific community has already addressed the skeptic arguments in some detail, there is still a public perception that scientists have been dismissive of the skeptic viewpoint, so the intention in this report is to correct the balance. The result is, we believe, a balanced, expert, and detailed assessment of the scientific case for climate change that will help investors navigate these extremely complex issues.
The paper’s clear conclusion is that the primary claims of the skeptics do not undermine the assertion that human-made climate change is already happening and is a serious long term threat. Indeed, the recent publication on the State of the Climate by the US National Oceanic and Atmospheric Administration (NOAA), analyzing over thirty indicators, or climate variables, concludes that the Earth is warming and that the past decade was the warmest on record. Quantifying cause and effect or projecting future conditions is always incomplete in a system as complex as Earth’s climate, Claimswhere multiple factors impact the observations. Conclusions are thus presented in terms of probabilities rather than dead certainties. This uncertainty is not always adequately explained in the public debate and, when discussed, can appear to be a challenge to the credibility of the field. However, uncertainty is an inevitable component in our understanding of any system for which perfect knowledge is unattainable, be it markets or climate.
To us, the most persuasive argument in support of climate change is that the basic laws of physics dictate that increasing carbon dioxide levels in the earth’s atmosphere produce warming. (This will be the case irrespective of other climate events.) The only way that warming can be mitigated by natural processes is if there are countervailing ‘feedback mechanisms’, such as cooling from increased cloud cover caused by the changing climate. A key finding of the current research is that there has so far been no evidence of such countervailing factors. In fact, most observed and anticipated feedback mechanisms are actually working to amplify the warming process, not reduce it.
Simply put, the science shows us that climate change due to emissions of greenhouse gases is a serious problem. Furthermore, due to the persistence of carbon dioxide in the atmosphere and the lag in response of the climate system, there is a very high probability that we are already heading towards a future where warming will persist for thousands of years. Failing to insure against that high probability does not seem a gamble worth taking.
Addressing the claims
|Global average temperatures have not risen since 1998.||In fact, the decade of 2000 to 2009 is the warmest since measurements have been made. Multiple factors affect global average temperatures, including the long-term warming trend from GHGs. This time-varying interaction of climate drivers can lead to periods of relatively stable temperatures interspersed with periods of warming. The anomalously high global average temperatures in 1998 associated with the El Niño have been followed by comparably high values that reflect a combination of long-term warming and shorter-term natural variability. Periods of relatively constant temperature are not evidence against global warming.|
|Climate researchers are engaged in a conspiracy: global warming is a hoax.||There is no evidence that scientists have engaged in alleged conspiracies. Three investigations discerned no scientific misconduct in emails stolen from University of East Anglia’s Climatic Research Unit. It has been claimed that the decline in the number of weather stations in the global network since the 1990s was due to purposeful removal, but there is no evidence to support this; furthermore, the reduction in number of stations reporting data has introduced no detectable bias in the trend of the global average temperature anomaly. The IPCC reports undergo significant scrutiny, but as is inevitable in a 3000-page document, that scrutiny sometimes fails to detect errors. The few errors identified in the latest IPCC report were primarily in referencing and not in content. Their existence does not support a conspiracy to misrepresent climate research.|
|Climate models are defective and therefore cannot provide reliable projections of future climate trends.||We do not rely only on models for our understanding of the effect of greenhouse gases on climate. Theory (i.e. the physics and chemistry of the planet’s atmosphere and ocean) and observations are the foundation of our ability to understand climate and to assess and quantify forcing and impacts. Models represent the most formal way in which to project and quantify future conditions. Despite well known limitations to climate models such as the uncertainties of clouds, aerosols, and spatial resolution, climate models are increasingly able to reproduce a range of physical processes and feedbacks. They unanimously predict warming with increasing greenhouse gases of a magnitude consistent with estimates independently derived from observed climate changes and past climate reconstructions.|
|The greenhouse gas signature (tropospheric hot spot) is missing.||Climate models predict that GHGs cause cooling in the stratosphere and warming at the surface and throughout the troposphere. Observations are consistent with these predictions. Furthermore, new measurements in the tropics suggest greater warming in the upper troposphere than at the surface, as predicted by the models. Although the tropospheric hot spot (signature) is not unique to greenhouse gas forcing, the new observational data lend support to climate simulations.|
|The Medieval Warm Period was just as warm as, or warmer than, today.||Northern hemisphere temperatures in the Medieval Warming Period (MWP) may have been comparable to today, but the estimates have high uncertainty because there are so few records and spatial coverage is spotty. However, a MWP warmer than the last decade does not challenge the case for anthropogenic warming.|
|Carbon dioxide levels increase after temperatures rise in the ice core records.||The correlation of records of atmospheric CO2 and Antarctic temperature over the past 800,000 years indicates that CO2 amplified the warming attributed to variability in Earth’s orbit in the transition out the ice ages. Different processes can and do affect climate concurrently.|
|Earth’s climate is driven only by the sun.||While Earth’s climate is undoubtedly driven by the sun, the sun is not the only factor that determines climate. The observations of warming since the second half of the 20th century cannot be explained by solar activity because it has been decreasing. Sunspots, areas of the sun’s surface that appear darker in a telescope, have been observed since the invention of telescopes in 1610. Although climate predictions from sunspots have long been attempted, the predictions have not held up.|
|Water vapor is the most prevalent greenhouse gas.||Water vapor plays a primary role in the natural greenhouse effect, but that does not diminish the impact of CO2-induced warming. The concentration of water vapor is a positive feedback: as the earth warms, the atmosphere can hold more water vapor, which, in turn, warms it further.|
|CO2 in the atmosphere is already absorbing all of the infrared radiation that it can.||Carbon dioxide in the atmosphere at pre-industrial levels already causes substantial radiation absorption. Anthropogenic increases in carbon dioxide concentration cause further absorption (over a broader range of wavelengths) and change the height distribution of the absorption. These effects generate warming and are fully incorporated in current climate models.|
|Climate sensitivity is overestimated in current climate models.||Climate sensitivity is defined as the change in global mean temperature that occurs in response to a doubling of atmospheric carbon dioxide. Values between 2 and 4.5oC are consistent with our understanding of forcing and past and present climate shifts. Lower estimates tend to disregard feedbacks, like water vapor, and delays associated with slower earth system components, like the ocean. Furthermore, sensitivity values below 2.5oC cannot explain the observed climate changes of the past.|
|Increasing carbon dioxide will stimulate plant growth and improve agricultural yield.||Plant growth is stimulated by increased levels of CO2 under equal conditions of temperature and availability of water and nutrients. However, altered growing conditions due to projected shifts in climate will likely counter the fertilization effect in large parts of the already food-insecure world. Experiments to quantify the impact of CO2 enrichment indicate that increased growth does not occur for all plant species and that nutritional content of crops is sometimes negatively impacted.|
|Human society and natural systems have adapted to past climate change.||Past climate changes have often been accompanied by migration, war, and disease. The growing human population will inevitably make environmental change more disruptive in the future, even in the face of increased technological prowess.|
- Last Update: 7.9.2010
Copyright © 2010 Deutsche Bank AG, Frankfurt am Main
While this is a copy of the Deutsche Bank document, it is not the original document and has no official or legal status whatsoever. The original document may be found on the Deutsche Bank website: