A landmark climate report released at the White House Tuesday shows that climate change is affecting every part of the United States.
“Summers on the whole have been getting hotter, wildfires have been starting earlier, rain is coming down in heavier downpours,” John Holdren, White House science advisor, said at a news conference this morning.
The Third National Climate Assessment is unique because it looks exclusively at the United States, breaking down impacts related to climate change into eight distinct regions: The Northeast, the Southeast, the Midwest, the Great Plains, the Southwest, the Northwest, Alaska, and Hawaii and the Pacific Islands.
“The bottom line is that climate change is not a distant threat,” Holdren said. He called the report the “loudest and clearest alarm bell to date.”
The more than 800-page report is available to view here. We’ve pulled out some of the key charts and messages.
One of the biggest concerns related to climate change is sea level rise, particularly for areas along the U.S. coastline and low-lying regions.
OBSERVATION AND PROJECTION: Global sea level has risen by about 8 inches since records began in 1880, the report said. It’s projected to rise by another 1 to 4 feet by the end of the century, with some scientists warning that an increase of 6 feet is even possible.
PROJECTION: The potential for disaster is greatest in coastal cities with dense populations, including places like New York City. This map shows areas in New York’s five boroughs that are expected to face increased flooding over the next 70 years. You can see the flood zone gets push farther inland over the coming decades, represented by the red, orange, and yellow shading.
OBSERVATION: One of the most surprising findings from the report is the increase in heavy downpours, particularly over the last five decades. As temperatures rise, there is more evaporation of water from oceans and soil. The water vapor in the atmosphere then comes down as rain or snow.
The colours on the map show how precipitation has changed in the continental U.S. between 1991 and 2010, compared to the average between 1901 and 1960. Most of the U.S. is getting more rain than ever before.
OBSERVATION: Not only is there more rain on the way for most of the states, but these storms will get stronger. The Midwest and Northeast are particularly at risk, with heavy rain events surging over the past half-century by 37% and 71%, respectively. The report warned that all regions of the U.S. can expect an increase in the frequency and intensity of heavy precipitation events.
PROJECTION: Extreme precipitation events — currently defined as a daily amount that only occurs once in 20 years — are expected to increase in the coming decades.
This map compares the number of extreme daily precipitation events by the end of the century compared to a period from 1981 to 2000. In a scenario where emissions are reduced (left), Americans can expect 1 to 2 extreme rain events every day. In a scenario where emissions increase (right), some of parts of the country can expect up to 7 extreme events on a daily basis.
OBSERVATION: In the U.S. alone, average temperature has increased by 1.3 to 1.9 degrees Fahrenheit since record keeping began in 1895. The colours on the map show how temperatures have changed in the continental U.S. between 1991 and 2010, compared to the average between 1901 and 1960. The deeper the red, the greater the change.
Temperature rise has not been the same across the country. The Great Plains, the Midwest, the Southwest, and the Northeast have experienced more warming than other parts of the nation. The bars on the regional graphs also show that temperature changes have not been constant. “Temperatures generally rose until about 1940, declined slightly until about 1970, then increased rapidly thereafter,” the report said. The year 2012 was the warmest on record for the contiguous U.S.
OBSERVATION: Over the past million of years the Earth has shifted between warm “interglacial” periods and cool “glacial” periods. These transitions occurred over long stretches of time and were caused by natural variation in the Earth’s system. The report stressed that what’s happening today is different: The climate is changing in ways that can’t be explained by natural variation alone. The period between 2000 and 2009 was “warmer than any time in at least the last 1300 years and perhaps much longer,” the report said.
This chart decouples the amount of warming caused by human activities from the Earth’s natural hot and cold extremes. The green band shows how the global average temperature would have changed over the last 100 years due to natural variations. The black line shows actual observed increases in global temperatures, which are only possible if you factor in heat-trapping gases released into the atmosphere by humans.
PROJECTION: The amount of climate change over the next few decades depends on the amount of heat-trapping gases that continue to be released into the atmosphere. Reducing levels of emissions now will result in less warming in the future. In order to limit a global temperature increase of 3.6 degrees Fahrenheit compared to pre-industrial levels, we would need to reduce emissions by more than 70% by 2050, the report said.
The map below shows how the average annual temperature is expected to change between 2071 and 2099 compared to the period between 1970 and 1999 under two different scenarios. The left image assumes there are rapid reductions in emissions and the right image shows what will happen if emissions continue to increase.
You can see even in the best case (and least likely) scenario the U.S. will still see 3 to 5 degrees of warming. If we continue “business as usual” it could be a 10 degree jump.
A Clearer Outlook
Scientists have a much greater understanding of climate change than they did a decade ago and since the last National Climate Assessment was released in 2009. Back in 2000, for example, sea level was projected to rise by around 10 to 17 inches, Tom Carl, the director of the National Oceanic and Atmospheric Administration’s National Climatic Data center, said at a press conference on Tuesday. Those estimates have now been updated to 1 to 4 feet by the end of the century. Sea ice is now expected to disappear by mid-century as opposed to the end of the century and more heavy precipitation events are expected. Other important advances in climate knowledge are highlighted in the chart below.