CLIMATE CHANGE: THE FACTS

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1 Fact 1: Carbon Dioxide is a Heat-Trapping Gas Proven in lab experiments as far back as First suggested as a cause of global warming, thanks to fossil- fuel burning, in around Fact 2: We Are Adding More Carbon Dioxide to the Atmosphere All the Time A steady increase in atmospheric concentrations of CO2 has been measured since the 1950 s with high- precision instruments on Mauna Loa, Hawaii. Amount of CO2 in the air back in 1800: about 270ppm (parts per million) Amount of CO2 in the air in the 1950 s: just over 300ppm Amount of CO2 in the air today: approaching 400ppm

2 Fact 3: Temperatures are Rising Overall, the Earth s average surface temperature is 1.3 F higher than it was a century ago. In the U.S., the average temperature has gone up by almost exactly the same amount. The 1990 s were warmer that the 1980 s. The 2000 s were warmer than the 1990 s. In the 1960 s, there were more record lows than record highs. In the 2000 s, there were more than twice as many record highs as record lows. Fact 4: Sea Level is Rising Sea level overall is eight inches higher today, on average, than it was in Locally, the rise may be lower or higher, depending on geology, ocean currents and other factors. Most of the rise so far comes from water expanding as the ocean temperature has increased. Experts expect the rise to accelerate as melting ice adds extra water to the seas. Higher sea level will make high tides and storm surges more damaging.

3 Fact 5: Climate change can be natural, but what s happening now can t be explained by natural forces Among the natural causes of climate change: Changes in the brightness of the sun Changes in the atmosphere when plants began converting CO2 to oxygen Continental drift, which created new patterns of circulation in the ocean Changes in the Earth s tilt, which alter the amount of sunlight in summer and winter Massive volcanoes spewing gases into the air Among the human causes of climate change: CO2 from burning fossil fuels Methane and nitrogen oxides from agriculture Deforestation, which cuts down on how much CO2 nature suck out of the atmosphere

4 Fact 6: We can already see the effects of climate change All sorts of observations point to a warming world besides rising temperatures and rising sea level. Among them: Tree lines are moving north (in the northern hemisphere) and to higher altitude Spring is coming earlier, and the frost- free season lasts longer in many places Glaciers and ice caps are shrinking around the world Birds and other species are migrating earlier in the spring and later in the fall

5 Fact 7: The terms global warming and climate change are almost interchangeable. Greenhouse gases raise the temperature, but when temperature changes, that can change lots of other things, including: Weather patterns Ocean currents Sea level The mix of species that lives at a given location The frequency of severe storms, heat waves and droughts

6 Fact 8: Global Warming is a long-term trend; it doesn t mean next year will always be warmer than the year before. In most parts of the U.S., the temperature warms from February to August, then cools from August to February. But that doesn t mean May 12 is always warmer than May 11, or that May is always warmer, on average than April. Hot and cold spells are normal; unusually hot or cold years, or even decades, don t mean there is no underlying trend.

7 Fact 9: Extreme weather events, including torrential rainstorms, droughts and heat waves, have become more common and more intense. Extreme events have always happened, so it can be hard to tell when they re happening unusually often. Nevertheless, the evidence suggests that intense storms, droughts and heat waves are coming more often, and with more intensity, than they did in the past. The evidence isn t as strong for floods or tornadoes.

8 Fact 10: Frost and snowstorms will still happen in a warmer world. Minnesota and Maine and Iowa and Pennsylvania and pretty much any place that gets ice and snow will see average winter temperatures warm up over the next 100 years. But these are just averages: some days will still plunge below freezing. It just won t happen as often. To eliminate below- freezing days entirely, the average winter temperature would have to go a lot higher than any climate model is projecting.