Northern Hemisphere snow cover has declined 10 percent in two decades, but no significant melting of the Antarctic ice sheet has been detected. Land surface Mountain ranges can block clouds, creating 'dry' shadows downwind. Sloping land allows more water runoff, leaving the land and air drier. A tropical forest will soak up carbon dioxide, but once cleared for cattle ranching, the same land becomes a source of methane, a greenhouse gas. Human influences Humans might be magnifying warming by adding to the greenhouse gases naturally present in the atmosphere.
Fuel use is the chief cause of rising carbon dioxide levels.
One of the most destructive droughts in recent memory is the 1930s American Dust Bowl, which lasted only six years. Researchers need to gather more data on past climates before this information can be used to accurately predict and design strategies for future large and persistent climate changes, says deMenocal, but acknowledging the historic impact of these severe events is an important step toward that goal. We now have to relearn history on a long-term scale. Ths website is designed and maintained in cooperation with HelpForMyWebsite.