Photo: Ian Joughin
A new study published Thursday in the journal Science provides the most definitive — and accurate — evidence yet that polar ice caps on Greenland and Antarctica are melting. Shrinking ice is not the only telltale sign that climate change is real. From rising air and ocean temperatures to stronger storms to record droughts, evidence of a changing global climate is all around us.
The Intergovernmental Panel on Climate Change (also known as the IPCC) has linked many of these changes in climate to an increase in greenhouse gas emissions from human activities, which was documented in a 2007 assessment report compiled by thousands of scientists over decades of research and debate.
Regardless of their causes – whether you believe in anthropogenic drivers, like fossil fuels from power plants and cars or not — the observed changes in climate are scientific facts that have grave implications for the future of natural and human systems.
Global temperature trends estimated by four different research groups all show a warming of the Earth over the past century, with particularly rapid increases through the past few decades.
Since 1901, global average surface temperatures have risen at an average rate of 0.13 degrees Fahrenheit per decade. The United States has warmed at nearly twice the global rate since the 1970s.
Average temperatures in January-October of 2012 were the highest in the continental U.S. (1.04 degrees Fahrenheit above normal) and the ninth highest worldwide, since records began in 1850.
Average Arctic temperatures have increased at almost twice the global average rate in the past 100 years.
This year, Arctic Sea ice measured 1.32 million square miles, which is 18 per cent less than the previous record low set in 2007.
Since 1960, glaciers worldwide (not including the ice sheets in Antarctica and Greenland) have lost more than 2,000 cubic miles of water, contributing to observed changes in sea level rise.
Since 1900, seasonally frozen ground has decreased by 7 per cent (up to 15 per cent in the spring) in the Northern Hemisphere. The time that lakes stay frozen has generally decreased at an average rate of one to two days per decade since the mid-1800s.
The portion of North America covered by snow has generally decreased since 1972. The average extent for the 1970s (1972 to 1979) was 3.43 million square miles, compared with 3.3 million for the 1980s, 3.21 million for the 1990s, and 3.18 million from 2000 to 2008.
Since 1901, global precipitation has increased at an average rate of 1.9 per cent per century (specifically in eastern parts of North and South America, northern Europe, and northern and central Asia), while precipitation in the lower 48 states has increased at a rate of 6.4 per cent per century. Climate change will also cause some areas to experience decreased precipitation such as in the Sahel, the Mediterranean, southern Africa, and parts of southern Asia.
Sea surface temperatures have been higher during the past three decades than at any other time since large-scale measurement began in the late 1800s. From 1901 through 2009, sea surface temperatures rose at an average rate of 0.12 degrees Fahrenheit per decade. Over the last 30 years, temperatures have risen more quickly at a rate of 0.21 Fahrenheit degrees per decade.
Three different studies show that ocean heat content (the amount of energy the ocean absorbs from the sun) has increased substantially since 1955. Ocean heat content not only determines sea surface temperature, but also affects sea level, currents, and the temperature on land.
Between 1993 and 2005 sea level rose, on average, 3 millimeters (0.1 inches) per year, attributed to an increase in melting ice and thermal expansion as the ocean absorbs more and more energy from the sun.
During the 20th century, sea level rose an average of 7 inches after 2,000 years of relatively little change. The 2007 IPCC report conservatively predicted that sea levels could rise 10 to 23 inches by 2100 if current warming patterns continue.
By looking at hurricane records, researchers saw that were almost twice as many Katrina magnitude events in warmer years than there were in colder years. Another study found that hurricanes, typhoons and tropical storms were intensifying more rapidly than 25 years ago.
A new study in the journal Science found that melting polar ice caps in Greenland and Antarctica raised sea levels by nearly half an inch over the last two decades. Combining satellite data from dozens of earlier studies, scientists not only have definitive proof that ice is melting, but that its happening much faster than expected.
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