Climate Science

Climate science encompasses a variety of disciplines that contribute to understanding of the Earth’s atmosphere and climate, including present and future anthropogenic climate change. Due to the complexity and size of the atmosphere and climate system, present-day understanding of the behavior of the Earth’s climate (and therefore future climate change) is based on contributions from a wide range of fields, including biology, ecology, atmospheric chemistry, volcanology, hydrology, geology, and meteorology, as well as engineering and quantitative analysis. Understanding and prediction of future climate change is based primarily on climate change models, which attempt to represent in detail the more deterministic aspects of the systems of interest, and make a range of assumptions regarding the less well understood or more chaotic aspects of the systems. For example, the long-term global warming effect of CO2 is reasonably well understood, but the effects of aerosols are less clear, and the future emissions (anthropogenic and natural) of each of these types of gases even less so (see figure).¹

Climate forcing by greenhouse gases and aerosols, with estimated uncertainty

Climate forcing by greenhouse gases and aerosols, with estimates of uncertainty (Click on thumbnail images below for large format)

Source: http://www.grida.no/climate/ipcc_tar...arge/06.01.jpg. Author: IPCC. Permission: IPCC.

Despite the complexity of the systems relevant to future climate change, there is overwhelming evidence that anthropogenic climate change is happening at present, its effects will get far worse in the future, and that mitigation and adaptation are already serious and urgent issues.²³⁴

History

As far back as the turn of the 20th century, scientists have speculated that increasing CO2 concentrations could produce global warming, including Svante Arrhenius (chemist), Alfred Lotka (physicist), and G. Evelyn Hutchinson (biologist).⁵ The first computer models that linked increasing concentrations of CO2 to warming were developed in the 1960's.⁶ The Mauna Loa observatory, set up by C.D. Keeling in 1958, has measured concentrations of atmospheric CO2 over time, continuing to the present day. This station has documented a steady average annual increase from 315 parts per million (ppm) in 1958 to the present concentration of 386 ppm,⁷ an average increase of more than 1 ppm per year. The importance of CO2 for climate change was confirmed quite conclusively from analysis of the Vostok Ice Core in 1987, which demonstrated an amazingly precise correlation between long-term historical atmospheric CO2 concentrations and the average surface temperatures on Earth (see figure).⁸

Trends in Atmospheric CO2 and Global Surface Temperature (Click on thumbnail images below for large format)

Source: http://www.pewclimate.org/docUploads...107_062554.gif. Author: Pew Center on Global Climate Change. Permission: Pew Center on Global Climate Change.

The last two decades have witnessed a boom in research related to climate change, documenting its effects, and predicting future changes to the biosphere and to human societies. Climate change has implications for almost all of the natural and social sciences. The Intergovenmental Panel on Climate Change, founded in 1988 and composed of thousands of independent researchers, generally coordinates the status of the scientific consensus on climate change, and serves as an interface between the scientific community and policy-makers. The IPCC recently released its Fourth Assessment Report (AR4), confirming an "unequivocal" warming trend over the last century, and forecasting further warming in the upcoming century.⁹

Climate Science and Policy

Climate science is integral for the development of climate policy. While some aspects of climate change mitigation may return economic or social benefits—e.g. market failures addressed by energy efficiency policies,¹⁰ or enhanced energy security owing to renewable energy deployment¹¹—it is generally accepted that stabilization or reversal of climate change will incur economic and social costs.¹² Climate policies should be designed to maximize climate-related benefits while minimizing these associated costs.¹³ The goal of the United Nations Framework Convention on Climate Change, ratified in 1993, is "stabilization of atmospheric concentrations of greenhouse gases at a level that would prevent dangerous anthropogenic interference with the climate system."¹⁴ However, the levels of global atmospheric greenhouse gas concentrations or radiative climate forcing that would achieve this aim are not known. Moreover, costs of large-scale reductions of greenhouse gas emissions are also not known, and different models' estimates of future mitigation costs vary by several orders of magnitude, even when the stabilization targets are similar.¹⁵ Therefore, future climate policies will be developed in tandem with the evolution of climate science, and enhanced sophistication of the models used as the basis of climate science.

Footnotes

¹IPCC (2001). Special Report on Emissions Scenarios. Intergovernmental Panel on Climate Change, Third Assessment Report.

²U.S. Climate Change Science Program (2008). The Effects of Climate Change on Land Resources, Water Resources and Biodiversity in the United States. Final Report, Synthesis and Assessment Product 4.3.

³IPCC (2007). Climate Change 2007: Synthesis Report. Intergovernmental Panel on Climate Change, Fourth Assessment Report.

⁴: Stern Review (2007). The Science of Climate Change: Scale of the Environment Challenge. Chapter 1 in: Stern Review: The Economics of Climate Change.

⁵Environmental Defense (2003). Global Warming: The History of an International Scientific Consensus.

⁶American Institute of Physics (2007). Introduction: A Hyperlinked History of Climate Change Science.

⁷Earth System Research Laboratory (2009). Trends in Carbon Dioxide - Mauna Loa. U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Earth Systems Research Laboratory, Global Monitoring Division.

⁸Barnola, J.-M., D. Raynaud, C. Lorius, and N.I. Barkov (2003). Historical CO2 record from the Vostok ice core. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A.

⁹ IPCC (2007), p.30.

¹⁰Lovins, Amory (2005). Energy End-Use Efficiency. Rocky Mountain Institute, Snowmass, CO.

¹¹Worldwatch Institute, Center for American Progress (2006). American Energy: The Renewable Path to Energy Security.

¹²IPCC (2007), Table 5.2.

¹³e.g., Wigley, T.M.L., R. Richels, and J. Edmonds (1996). Economic and Environmental Choices in the Stabilization of Atmospheric CO2 Concentrations. Nature 379: 240-243.

¹⁴United Nations Framework Convention on Climate Change (1993). Full Text of the Convention, Article 2: Objective.

¹⁵e.g., U.S. Climate Change Science Program (2007). Scenarios of Greenhouse Gas Emissions and Atmospheric Concentrations. U.S. Climate Change Science Program, Synthesis Product 2.1A, Table 4.5.