Global Change Topic 7 Part 1 The Earth Greenhouse NPS Naturally © occurring CO2, H2O, N2O, and CH4 help to keep the earth warm. This supports life. The problem: humans produce lots more of these gases than naturally occur, plus CFCs and tropospheric ozone. This is trapping more heat than would occur naturally at this point. Greenhouse gases Other factors that affect the earth's temperature Oceans Cloud cover Air pollution levels Photosynthesis levels Volcanoes and climate Historic climate The Medieval Warming Historic Temperature and CO2 Proxies Species composition Ice cores Oxygen isotope ratios Foraminifera Trends in greenhouse gas concentrations Sun Carbon (and some heat) sources and sinks Troposphere Aerosols Greenhouse gases Cooling from increase Warming from decrease CO2 removal by plants and soil organisms CO2 emissions from land clearing, fires, and decay Heat and CO2 removal Heat and CO2 emissions Ice and snow cover Shallow ocean Land and soil biota Natural and human emissions Long-term storage Deep ocean Fig. 20-6, p. 469 Current trends Earth is getting warmer: the temperature has been well above normal for more than 25 years. Current trends Grinnell Glacier, Glacier National Park 1900 and 2008 Snow and ice are melting at rates unseen for thousands of years. In Glacier National Park, for example, there were 150 glaciers in 1850. Today, there are 26. Current trends Arctic ice in the summer Sea ice is dwindling, especially in the Northern Hemisphere. Satellites have seen average Arctic sea ice shrink by 2.7% per decade from 1978 to 2006, with faster melting in summer. Positive feedback loops increase warming Melting of polar sea ice Melting of glaciers Shorter winters in the tundra (methane release) Negative feedback loops can temporarily slow warming Predictions Climate change effects Rising Sea Levels Species range and seasonal behavior shifts Some bird species are already showing shifts in seasonal habits. Other early signs: Plants are flowering early than normal, some pollinators are missing out Some insects are emerging before bird eggs hatch Plankton are shifting ranges, affecting the rest of their food chains Increased ocean acidity, degradation of coral reefs Climate change: impacts on people In a warmer world, agricultural productivity may increase in some areas and decrease in others. Crop and fish production in some areas could be reduced by rising sea levels that would flood river deltas. Reduce drinking water supplies Global warming will likely increase deaths from: Heat and disruption of food supply. Spread of tropical diseases to temperate regions. Increased number of environmental refugees.