Climate Finance: Regulatory and Funding Strategies for Climate Change and Global Development

Chapter 2 Understanding the Causes and Implications of Climate Change

Climate Finance 35 Chapter 2 Understanding the Causes and Implications of Climate Change Michael Oppenheimer Albert G. Milbank Professor of Geosciences and International Affairs, Woodrow Wilson School and the Department of Geosciences, Princeton University Key Points • Carbon Dioxide (CO2)—emitted through electricity generation, transport, agriculture, and forestry—is responsible for four-fifths of the warming effect of current emissions of long-lived greenhouse gases and will persist in the atmosphere for many decades, with a significant fraction remaining for more than a millennium. CO2 levels are already higher than any time in at least the past 850,000 years. • While the effects of climate change cannot be predicted with certainty because future emissions trajectories are not known and our understanding of the climate system (particularly feedbacks) is limited , we are already seeing significant climatic impacts, including: increasing mean ocean temperature and sea level; increasing extremes of heat and drought; changes in ranges of species; melting of ice sheets, Arctic sea ice, and glaciers; and increasing severity of some extreme climatic events. Causes of Climate Change The basic scientific framework of the climate change issue is well understood : greenhouse gases (GHG) emitted in the process of electricity 36 Michael Oppenheimer generation, transport, agriculture, and forestry are accumulating in the atmosphere, gradually altering the heat balance of the Earth and inevitably changing its climate. The greatest concern arises from long-lived gases (carbon dioxide, methane, halocarbons, and nitrous oxide) because they persist in the atmosphere for a period ranging from decades to longer than a millennium after release. Of these, carbon dioxide is the most important because it accounts for about four-fifths of the warming effect of current emissions of the long-lived GHGs. Atmospheric carbon dioxide levels are already one-third greater than in preindustrial times, and higher than at any time in at least the past 850,000 years. Other trace constituents emitted from human activity affect the climate in important ways, but are much less persistent. These include ozone (a key component of smog) and soot and other particles, the latter having both warming and cooling effects. All this we know with certainty. It is also certain that over the past century, the Earth has warmed by about three-fourths of a degree Celsius (°C). It is very likely that the combined influence of all these gases and particles has caused most of the observed warming of the past halfcentury . Carbon dioxide from the combustion of fossil fuels (coal, oil, and natural gas) for electricity generation, transport, and other purposes produces almost 60% of the warming effect of the current emissions of long-lived gases. Another 20% comes from carbon dioxide and other gases emitted during the cutting and burning of forests for the purposes of conversion of lands for timber production, agriculture, pastoral use, and related settlement . Climate change cannot be slowed significantly, and the climate cannot be stabilized, without large reductions in emissions from fossil fuels and strong measures to curb deforestation. Consequences of Climate Change There are two general sources of uncertainty in projecting future climate change. First, estimates of future emissions of the greenhouse gases vary widely, although most projections envision emissions continuing to grow for at least the first half of this century. The second source of uncertainty arises from our limited understanding of the climate system, particularly the responses (called feedbacks) of the individual components of the 37 Fig. 2.1. Changes in temperature, sea level, and Northern Hemisphere snow cover. Observed changes in (a) global average surface temperature, (b) global average sea level from tide gauge and satellite data, and (c) Northern Hemisphere snow cover for March– April. All differences are relative to corresponding averages for the period 1961–1990. Smoothed curves represent decadal averaged values, while circles show yearly values. The shaded areas are the uncertainty intervals estimated from a comprehensive analysis of known uncertainties (a and b) and from the time series (c). (Source: Climate Change 2007: Synthesis Report; Contribution of Working Groups I, II, and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Figure SPM.1, IPCC, Geneva, Switzerland) 38 Michael Oppenheimer Earth system—including clouds, ice sheets, and ocean circulation—to the initial greenhouse warming. The range of possibilities is enormous. If prompt action is taken to stem emissions, it remains possible that a modest additional global warming of not much more than 1°C would occur. Even if limited...