References:

Intergovernmental Panel on Climate Change – Climate Change 2007: The Physical Science Basis, Summary for Policy Makers; 2007

Is climate change really happening?

Yes. In February 2007, the Intergovernmental Panel on Climate Change (IPCC) reported to the United Nations that the Earth’s climate system is undoubtedly getting warmer.

According to the Climate Impacts Group at the University of Washington, the average annual temperature in the Pacific Northwest rose by 1.5° F in the 20th century and is expected to rise 0.5° F per decade in the first half of the 21st century.

The graph below shows the global annual temperature change since 1880. Even with variation over the years, the general trend is clearly upward. Some cooler temperatures in recent years have prompted people to ask if there is now a global cooling trend, but as the graph shows, even several years of cooling doesn’t mean a long-term warming trend is over.

The land-ocean temperature index combines data on air temperatures over land with data on sea surface temperatures. (“Mean” is the midpoint between the highest and lowest.) The black line shows the annual changes; the red line tracks 5-year periods. Source: NASA Goddard institute for Space Studies. (January 11, 2008)

Although specific, individual events can’t be directly linked to global warming, the IPCC has noted many indications of climate change around the world:

• Retreating mountain glaciers on all continents

• Thinning ice caps in the Arctic and Antarctic

• Rising sea level – about 6-7 inches in the 20th century

• More frequent heavy precipitation events (rainstorms, floods or snowstorms) in many areas

• More intense and longer droughts over wider areas, especially in the tropics and subtropics

References:

Intergovernmental Panel on Climate Change – Climate Change 2007: The Physical Science Basis, Summary for Policy Makers; 2007

What causes climate change and global warming?

This question has been debated a lot, because climate change can be “due to natural variability or as a result of human activity” (IPCC 2007) and because the climate system is very complex.

There is new and stronger evidence that most of the warming over the last 50 years is due to human activities. Ice cores taken from deep in ancient ice of Antarctica show that carbon dioxide levels are higher now than at any time in the past 650,000 years. More carbon dioxide in the atmosphere means warming temperatures. In its 2007 report to the United Nations, the Intergovernmental Panel on Climate Change (IPCC) concluded that it is more than 90 percent likely that the accelerated warming of the past 50-60 years is due to human contributions.

These contributions include increased levels of “heat-trapping” gases (a.k.a. “greenhouse gases”) such as carbon dioxide in the Earth’s atmosphere. One of the biggest ways people contribute to greenhouse gases is by burning fossil fuels. We use coal, oil, and natural gas to generate electricity, heat our homes, power our factories, and run our cars.

Changing land use patterns contribute, too. Trees and other plants use carbon dioxide and give off oxygen. When trees are cut down for development, agriculture, and other purposes, they’re no longer available to take carbon dioxide out of the air, and actually release carbon dioxide as they decay or burn.

As the levels of carbon dioxide and other greenhouse gases increase, more heat is “trapped” and global temperatures rise. This causes significant changes in the timing and length of the seasons as well as the amount and frequency of precipitation. (IPCC 2007)