Global Warming is Happening Now
No longer is global warming something only facing future generations. Changes to our climate are being documented all across the planet today. People, animals, and plants are already feeling the heat. The Earth's atmosphere has already warmed by 1.5 degrees Fahrenheit since 1900. This warming signal is also found in ocean temperatures, soil temperatures, melting glaciers and melting polar ice caps. It has been linked to widespread impacts on ecosystems around the planet. This preponderance of evidence all points to the conclusion that our planet is warming and natural systems are struggling to keep up.
Temperatures are increasing
The most striking evidence of a global warming trend is closely scrutinized data that show a relatively rapid and widespread increase in temperature during the past century. The 10 warmest years on record occurred during 1997-2008, according to NASA's Goddard Institute for Space Studies.
The rising temperatures observed since 1978 are particularly noteworthy because the rate of increase is so high and because, during the same period, the energy reaching the Earth from the Sun had been measured precisely enough to conclude that Earth's warming was not due to changes in the Sun.
Sea levels are rising
Global sea level has increased by roughly 8 inches over the past century, and the rate of increase is accelerating. Global warming causes sea-level rise in two ways: (1) Ocean water is expanding as it warms. (2) Land-based ice in glaciers and ice sheets is melting.
Sea-level rise has been happening even faster than scientists anticipated a few years ago. If recent projections are accurate, 2-3°F warming could bring about 3 feet of global sea-level rise by 2100, displacing approximately 56 million people in 84 developing countries around the world. Coastal habitats also face major changes as low-lying areas are inundated with saltwater.
Sea ice is melting
Declining sea ice is one of the most visible signs of global warming on our planet. Since 1979, Arctic sea ice extent in September (when the annual minimum is reached) has declined by over 30 percent, according to the National Snow and Ice Data Center. The ice extent has been declining in other seasons, too. Despite slightly larger ice extents in 2009, recent observations indicated that the ice is thinner and much younger (less multiyear ice) than it used to be.
Covering an average of 9.6 million square miles, these areas of ice floating on ocean waters play an important role in regulating our climate, by reflecting some sunlight back to space, and in the life cycles of many polar species, such as polar bears, seals, and walruses.
Precipitation patterns are changing
Some places are getting more rainfall and others are getting less. Nearly everywhere is experiencing more heavy rainfall events, as warmer air is able to hold more water vapor.
Right here in the United States, we are already seeing some important trends in precipitation. The Southwest appears to be shifting to a more arid climate, in which Dust Bowl conditions will become the new norm. Annual precipitation totals in the Northeast, Midwest, and Plains have increased by 5 to 20 percent during the last 50 years. The southeastern United States is having both more drought and more floods.
Oceans are acidifying
The ocean has absorbed a large fraction of the carbon dioxide fossil fuel burning has pumped into the atmosphere, slowing the rate of global warming. But, all this extra carbon dioxide is impacting the ocean, too. The pH of surface seawater has decreased by 0.1 units since 1750, and is projected to drop another 0.5 units by 2100 if no action is taken to curb fossil fuel emissions. These changes would take tens of thousands of years to reverse.