Some final concluding thoughts about the unavoidable complexities of climate science and the need to confront uncertainties and inconsistencies. Some respected scientists question the seriousness of climate risks and as the discussion forums illustrate, this can make for quite heated debate. At the risk of fueling the fire, I have a few observations based on more than 30 years engaged in this issue:
· The basic features of the greenhouse effect are matters of atmospheric physics known for over a century and proven by examination of other planets. The atmosphere of Venus is almost completely comprised of carbon dioxide and consequently the temperature over the surface is more than 470C! Put enough CO2 into the atmosphere and the temperature will go up – there is no debate about it.
· The study of climate change involves many different disciplines such that no one person is expert in all of them. Consequently assessments by collections of experts such as the Intergovernmental Panel on Climate Change and National Academy of Sciences in the U.S. are essential. When such assessments involve hundreds of scientists reviewing thousands of articles and are updated periodically, the likelihood of significant bias or distortion in one direction is minimized (although never completely eliminated – scientists make mistakes too!).
· Whether referred to as “climate change”, “global warming”, or the “greenhouse effect”, the phenomenon describing the consequences of increasing the concentration of atmospheric gases absorbing solar radiation cannot be reduced to a single metric or indicator. While global average temperature is the most widely cited and readily understood metric, it is only one of many indicators used to measure and validate predicted changes in the earth’s climate system. Others include glacial melting, changes in precipitation patterns, ocean heat content, and sea level rise. The conclusion that climate change is occurring rests on an assessment of all these indicators.
· The climate system has many lags such that emissions today will have impacts not fully realized for several decades. However once they occur such changes will be persistent and effectively irreversible for centuries. Thus decisions will have to be made in the absence of full knowledge as once the impacts become apparent it will be too late to reverse them. (This is the logic that underlies the “precautionary principle”, which states that if an action may cause significant but uncertain harm, the burden of proof that it is not harmful falls on those taking the action.)
· -While there are many sources of uncertainty when making projections of climate change, the greatest source of uncertainty is us – the choices we make as a society about energy use and supply, where we live and work, and the design of buildings. These choices can accelerate and exacerbate the risks or delay and lessen them.
· -The benefits of the activities that contribute to climate change are immediate and short-term, while most of the risks will have disproportionate impact on future generations. This generational disconnect is difficult to evaluate in conventional economic terms and is increasingly being discussed as a moral and ethical issue as reflected in a forthcoming Papal Encyclical on climate change.
· – Many of the actions that need to be taken to reduce greenhouse gas emissions and enhance climate resilience have minimal costs and significant co-benefits such as reducing air pollution and protecting communities against floods and other extreme weather events. The World Bank is among many financial institutions who increasingly see the need to be “climate smart” for development to be sustainable.
My final thought is don’t be discouraged despite the seriousness of the climate challenge. The future is still very much for all of us to determine!