The Intergovernmental Panel on Climate Change (IPCC) has a rich repository of figures and data, and because these data are likely to influence some policy actions in your future, its worthwhile taking a few minutes to look at the IPCC reports.
The most brief and to the point is the Summary for Policy Makers (SPM) that accompanies the fourth Assessment Report. You can find the summary at www.ipcc.ch/ipccreports/ar4-syr.htm. If you have time, the full report is also available at this site.
Open the SPM and look at the first page of text, then look at the first figure, SPM1 (reproduced here). Look at this figure carefully and answer the following questions:
Carefully read the caption. What does the area between the blue lines represent? Why are the blue lines shown in this report?
Changes in temperature, sea level and Northern Hemisphere snow cover

See the evidence: view the IPCC report at www.ipcc.ch/graphics/syr/spml.jpg.

(a) Global average surface temperature 14.5 14.0 13.5 (D) Global average sea lovel 50 -50 -100 -150 (c) Northern Hermisphere snow cover 40 36 32 1850 1950 2000 1900 Year Dference from 1961-1990 (million km) Temperature ("C) (uu)