Climate Basics

References & Reading

Managing Lands Under Climate Change has been modified from:

Millar, C.I.; Stephenson, N.L.; Stephens, S.L. 2007. Climate change and forests of the future: managing in the face of uncertainty. Ecological Applications. 17: 2145-2151. http://treesearch.fs.fed.us/pubs/31774

Expected Effects in the U.S.

Temperature and Precipitation Projections

Global average temperatures are projected to rise over this century. Temperature increases will vary regionally and seasonally; for example, temperature increases at polar latitudes are expected to be greater than increases near the equator (IPCC 2007a Ch.11). Part of this future warming is inevitable due to the long-lived greenhouse gases that are already present in Earth's atmosphere. However the full extent of warming will depend in part on future emissions of greenhouse gases.

Natural Climate Cycles

Climate varies without human influence, and this natural variation is a backdrop against which human- caused climate change occurs. These patterns hold important lessons for understanding the magnitude and scope of current and future climate changes.

Cyclical variations in the Earth's climate occur at multiple time scales, from years to decades, centuries, and millennia. Cycles at each scale are caused by a variety of physical mechanisms. Climate over any given period is an expression of all of these nested mechanisms and cycles operating together.

Climate Mechanisms

The Greenhouse Effect

The physical mechanisms that cause greenhouse gases to warm the planet, commonly known as the 'greenhouse effect', are well understood and were scientifically demonstrated beginning in the mid-1800s (Tyndal 1861). Of the solar energy that is directed toward Earth, about 30% is reflected back to space by clouds, dust, and haze (Ramanathan & Feng 2009). The remaining 70% is absorbed by the atmosphere and the Earth's surface.

Current Climate Change

Global Warming and Rising CO2

Global average surface temperatures have increased markedly over the last century (Figure 1). Humans have been measuring temperature directly since the mid- 1800's; these measurements show that temperature increased by 1.33°F (0.74°C ) between 1906 and 2005, and that the rate of warming is increasing (IPCC 2007a Ch.3). The decade from January 2000 to December 2009 was the warmest decade during this time period (NASA 2011).

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