Where do we stand on global warming?
Global temperatures have risen by ~0.8\textdegreeC since the end of the 19th century. This increase has not been linear, as there have been periods when temperatures were stable for short periods before rising once again. The reasons for these changes in the rate of temperature rise are related to anthropogenic factors (sulphate aerosol pollution versus greenhouse gas inputs to the atmosphere) as well as to natural factors (volcanic eruptions, solar irradiance variations, El Ni\~no/Southern Oscillation [ENSO] fluctuations, etc). Over the last decade or so, temperatures have not risen at the same rate as in previous decades, and this has led to speculation that global warming is over. This view has been reinforced by the unusually cold winter that many parts of the United States and western Europe experienced in recent months. However, such a conclusion ispremature. The winter of 2009-2010 was one of the warmest on record when the entire globe is considered, and the last decade was the warmest, globally, for many centuries. In spite of these facts, many politicians who do not favor controls on carbon emissions have seized upon the recent conditions to present a one-sided view of the situation to the public. This effort has been reinforced by a relentless campaign to find and publicize a few errors in the Intergovernmental Panel on Climate Change (IPCC) 4th Assessment Report, to shake the public's confidence in that Report's main conclusions. Nevertheless, while the political bickering goes on, the levels of carbon dioxide and other greenhouse gases in the atmosphere continue to increase, more heat accumulates in the oceans, sea-level keeps rising as glaciers and ice caps melt, and phenological indicators from many regions demonstrate disruptionsto the seasonality of biological activity. And as these changes occur, world population keeps increasing, at a rate of ~240,000 people per day, most of whom will grow up to be subsistence or small-scale agriculturalists, who will be just as vulnerable to climatic anomalies as late prehistoric/early historic societies were. Climatologists, and other environmental scientists have a responsibility to ensure that the public, and the politicians they elect, fully understand these issues so that they can better appreciate the consequences of inaction over controlling greenhouse gas emissions.