Symptoms and Driving Factors of Contemporary Earth Warming and Projections for the Future

Abstract

This paper outlines the symptoms of contemporary global warming, reviews its possible driving factors and presents some projections for future. Key among the symptoms are those related to temperature, with the increase in average global temperature since 1880 now reaching a value of 0.85°C. While warming has encompassed almost the whole world, the high latitudes have warmed more than the low, and maximum temperature has increased more than average temperature. Warming has been causing sea level rise, thanks to both the thermal expansion of warming water and the melting of ice on land. The other consequence of warming is a change in precipitation pattern, manifesting itself in higher precipitation in certain parts of the world (generally at low and high latitudes), but also lower precipitation in other parts (mainly the Tropics); as well as in changes in the intraannual course characterising precipitation (with more falling in winter and less in summer), and in the frequency and intensity of rainfall (more intense heavy-precipitation events and higher variability where the frequency of precipitation is concerned). Among the possible driving factors, the most important are those related to the increase of CO2 and mixing ratios of other greenhouse gases in the troposphere. Land-use changes and emissions of aerosols to the atmosphere also exert a major impact on temperature. These are mainly anthropogenic factors. While natural drivers also modulate the climate markedly, they tend to warm and cool the globe alternately, stepping up warming when they are in a warming phase, but slowing down or even offsetting warming during a cooling phase. Projections for the future are entirely dependent on socio-economic scenarios of future development. All the (economically) realistic scenarios point to a continuation of the warming trend, with a further intense sea-level rise and precipitation changes, albeit with the rate of change varying in line with the rate of increase in concentrations of the greenhouse gases. The realistic range of values for average rise in global temperature is between 2 and even 6 degrees Celsius.