Climate and Global Change

Warm near the equator and cold at the poles, our planet is able to support a variety of living things because of its diverse regional climates. The average of all these regions makes up Earth's global climate. Climate has cooled and warmed throughout Earth history for various reasons. Rapid warming like we see today is unusual in the history of our planet. The scientific consensus is that climate is warming as a result of the addition of heat-trapping greenhouse gases which are increasing dramatically in the atmosphere as a result of human activities.

Earth's global average surface <a
  href="/earth/climate/ipcc_feb2007.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">warming</a> relative to the
  1980-1999 average over the past 100 years is shown in the black line.
  Predictions of the amount of warming in the future are shown by the red,
  green, and purple lines. These predictions, developed with <a
  href="/earth/climate/cli_models.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">computer models</a>, make different
  assumptions about how many <a
  href="/earth/climate/cli_greengas.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">greenhouse gases</a> we release into the
  atmosphere in the future.<p><small><em> A Windows to the Universe image based on a graph from the IPCC 4th Assessment Report</em></small></p>Roaming across Arctic <a
  href="/earth/polar/sea_ice.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">sea ice</a>, <a
  href="/earth/polar/polar_bears_jan07.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">polar
  bears</a> peer through cracks in the ice to look for ringed seals, their
  favorite food, in the water below. Almost all of a polar bear's food comes
  from the sea. The <a
  href="/earth/polar/sea_ice.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">floating sea
  ice</a> is a perfect vantage point for the bears as they hunt for food.
  Unfortunately, the amount of sea ice floating in the <a
  href="/earth/polar/polar_north.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">Arctic
  region</a> is shrinking each year, and getting farther apart.<p><small><em>Image courtesy of Ansgar Walk.  Creative Commons Attribution-Share Alike 2.5 Generic license.</em></small></p>Coral animals build reefs in warm, tropical seawater. However, <a href="/earth/changing_planet/ocean_temperatures_intro.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">seawater can be too warm</a> for their liking.  If waters get too warm, coral animals lose the algae that live within their little bodies, a process called coral bleaching. Without the algae, corals have less nutrition. Unless cooler temperatures return, allowing algae to
 return, the coral dies.<p><small><em>Credit: UNC</em></small></p>As temperatures rise and soil moisture decreases, plants are stressed, which can lead to <a href="/earth/climate/crops_withering.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">crop withering</a>. <a href="/teacher_resources/online_courses/health/events_health.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">Droughts</a> accompanied by increased temperatures can lead to famine, social and political disruptions. Scientists are  helping with early identification of drought that might trigger food shortages. Watch the NBC Learn video - <a href="/earth/changing_planet/withering_crops_intro.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">Changing Planet: Withering Crops</a> to find out more.<p><small><em>Image taken by Tomas Castelazo, Creative Commons <a href=&quot;http://creativecommons.org/licenses/by/3.0/deed.en&quot;>Attribution 3.0 Unported</a> license.</em></small></p>A <a href="http://iopscience.iop.org/1748-9326/8/2/024035/article">study</a> of over 40,000 written entries in Irish Annals and ice core measurements shows a strong correlation between <a href="http://www.windows2universe.org/earth/interior/eruptions.html">volcanic eruptions</a> and extreme cold weather in Ireland over a 1200 year period, from 431 to 1649.  During this time up to 48 volcanic eruptions were identified in Greenland ice core records through deposition of volcanic sulfate in annual layers of ice. Find out more about <a href="http://www.windows2universe.org/earth/climate/geosphere_volcanoes_influence_on_climate.html">volcanoes and climate</a>.<p><small><em>Image Courtesy of Marco Fulle</em></small></p>Scientists are concerned that melting Arctic sea ice will increase the amount of fresh water in the <a href="/earth/polar/arctic_currents.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">Beaufort Gyre</a>, which could spill out into the Atlantic and cause major climate shifts in North America and Western Europe. Watch the <a href="/earth/changing_planet/freshwater_arctic.html&edu=elem&dev=1/earth/Atmosphere/moons/triton_atmosphere.html">Changing Planet: Fresh Water in the Arctic video</a>.<p><small><em> Courtesy of Jack Cook, WHOI (<a href="http://www.whoi.edu">Woods Hole Oceanographic Institute</a>)</em></small></p>

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