The chart on the left shows
historical sea level data derived from coastal tide gauge records (trend
calculated using the linear regression method). The chart on the right shows
the average sea level since 1993 derived from global satellite measurements, updated
here monthly. Sea level rise is caused by the thermal expansion of sea water
due to climate warming and widespread melting of land ice.
Arctic Sea
Ice
September Arctic sea ice is now
declining at a rate of 11.2 percent per decade, relative to the 1979 to 2000
average.1
Arctic sea ice reaches its minimum extent each September. The graph on the left
charts the average September extent from 1979 to 2009, derived from satellite
observations. The illustration on the right shows the Arctic sea ice minimum
extent for 2009, which was the third-lowest in the satellite record.
Carbon dioxide (CO2) is
an important greenhouse gas released through natural processes such as
respiration and volcano eruptions and through human activities such as
deforestation and burning fossil fuels. The chart on the left shows the CO2
levels in the Earth's atmosphere during the last three glacial cycles, as
reconstructed from ice cores. The chart on the right shows CO2
levels in recent years, corrected for average seasonal cycles.
This graph illustrates the change in global surface temperature relative to
1951-1980 average temperatures. As shown by the red line, long-term trends
are more apparent when temperatures are averaged over a five-year period. The
green error bars represent the uncertainty on measurements. January 2000 to
December 2009 was the warmest decade on record. (Source: NASA/GISS)
Daily maximum for 2009:
24 million square km (9.3 million square miles)
on September 17
The "ozone hole" is a
severe depletion of the ozone layer high above Antarctica. It is primarily
caused by human-produced compounds that release chlorine and bromine gases in
the stratosphere. The ozone layer acts to protect life on Earth by blocking
harmful ultraviolet rays from the sun.
The image at left is a view of the
most recent Antarctic ozone hole, derived from satellite measurements that
monitor the ozone layer. The blue and purple colors are where there is the
least ozone, and the greens, yellows, and reds are where more ozone is
present.
There are signs that ozone
depletion is slowing in response to the 1987 Montreal Protocol, which
resulted in a significant reduction in global emissions of ozone-depleting
chemicals. However, climate change may cause the ozone hole to expand
further.
