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Climate change isn't just a problem for future generations — it's already affecting broad swaths of the United States.
That's the upshot of the National Climate Assessment, a massive new US government report detailing the current and future impacts of global warming around the country. The report is particularly useful in detailing how specific regions and sectors will be affected — and outlining some possible ways we could adapt.
There's a lot of information in the report, but here are nine highlights:
1) Most of the country is getting hotter
Temperature changes over the past 22 years (1991-2012) compared to the 1901-1960 average, and compared to the 1951-1980 average for Alaska and Hawai‘i. NOAA NCDC / CICS-NC.
This map is the simplest way to see global warming in action. Since the 19th century, average US temperatures have risen by 1.3°F to 1.9°F. (Note, though, there have been some fluctuations here and there: in the 1960s and 1970s, temperatures dipped, partly due to the cooling effect of sulfate pollution that was eventually cleaned up.)
Recent decades have been even hotter: since 1991, virtually every part of the country has been warming, with the biggest temperature increases occurring in the winter and spring.
2) The heaviest storms are getting wetter
Percent increases in the amount of precipitation falling in very heavy events (defined as the heaviest 1% of all daily events) from 1958 to 2012 for each region of the continental United States. Source: Karl et al. 2009.
As the atmosphere heats up, it can hold more water vapor. That, in turn, can lead to heavier precipitation — although this varies region by region.
Since the 1950s, the amount of rain or snow falling in heavy storms has increased in the Northeast, Midwest, Southeast, Great Plains, and Alaska — more than can be explained by natural variation. (It's less clear that there's a significant trend in the Southwest, Northwest, or Hawaii.)
By the way, this is just heavy precipitation — the report doesn't find any trend in the United States for a few other severe weather events, including tornadoes or hurricanes or even floods.
3) Sea levels are rising particularly fast along the East Coast
Local sea level trends in the Northeast region. Length of time series for each arrow varies by tide gauge location. NOAA.
Sea levels have risen, on average, about 8 inches around the world in the past century. But in some places, the ocean is rising even faster.
In the Northeast, for instance, sea levels have already risen about a foot over the past century. Levels are rising faster partly due to "land subsidence" — coastal land is actually sinking due to development or groundwater pumping. There's also a theory that changes in ocean circulation are also playing a role here.
Either way, more sea-level rise means more coastal flooding — particularly when storms strike. The report notes that two feet of sea-level rise would triple the rate of dangerous flooding throughout the Northeast.
4) The Southeast is getting more 95°F days
Projected average number of days per year with maximum temperatures above 95°F for 2041-2070 compared to 1971-2000, assuming emissions continue to grow (A2 scenario). NOAA.
In the Southeast, the number of days above 95°F has been increasing since 1970. (The number of nights above 75°F has also increased.)
Expect even more sweltering days if the planet keeps warming. As the map above shows, if greenhouse-gas emissions keep rising unchecked, the number of days above 95°F in the DC region could triple by mid-century. Florida would see an especially sharp rise in extremely hot days.
5) Snowpack is dwindling in the Southwest — putting water supplies at risk
Snow water equivalent (SWE) refers to the amount of water held in a volume of snow. Figure shows projected snow water equivalent for the Southwest, as a percentage of 1971-2000, assuming continued increases in global emissions (A2 scenario). Scripps Institution of Oceanography.
The Southwest's water supply relies on snow melting slowly from the mountains during the spring and summer. Over the last 50 years, however, a combination of climate change and increased dust and soot have been disrupting this system — there's less snow falling in the mountains, and melting is happening more quickly.
As the map above shows, that snowpack is expected to keep dwindling — posing risks to the water supplies needed to maintain the Southwest's cities, farms, and ecosystems. Many states will have to figure out better ways to conserve water if they want to adapt.
6) Farming in the Midwest has gotten a boost — for now
Projections are from global climate models that assume emissions of heat-trapping gases continue to rise (A2 scenario). NOAA.
Climate change hasn't been all bad so far. The report notes that warmer temperatures have lengthened the growing season in the Midwest by almost two weeks since 1950. What's more, higher concentrations of carbon-dioxide in the atmosphere have helped boost plant growth.
Those benefits are expected to last another few decades. But climate change will also have negative impacts that will start to hurt agriculture. An increased number of extremely hot days could damage crops. And heat waves during pollination could reduce corn and soy yields.
As such, the report recommends that farmers in the Midwest start preparing for projected climate impacts now — before the negative impacts start dominating.
7) Rivers in the Northwest are shifting in strength
The fraction of annual flow occurring in June increased slightly in rain-dominated coastal basins and decreased in mixed rain-snow basins and snowmelt-dominated basins over the period 1948 to 2008. Source: Adapted from Fritze et al. 2011.
The report notes that the flow in many of the Northwest's rivers has shifted over time — thanks to increased rain on the coasts and decreased snowmelt in the mountains.
The region will have to adapt. Some regions will see increased flood risk in the spring as a result of climate change. Other regions, by contrast, will have to deal with decreased river flow — that could hamper the effectiveness of hydroelectric dams or put a strain on farms in the region. Reduced river flow could also threaten key freshwater species like salmon and trout.
8) Summer sea ice in the Arctic is vanishing
Average September extent of Arctic sea ice in 1980, 1998, and 2012. September is typically the month when sea ice is least extensive. Inset is the complete time series of average September sea ice extent (1979-2013). NSIDC.
The map above shows the reduction in summer sea ice in the Arctic as the planet has been warming.
That has all sorts of surprising effects: The Arctic is now becoming more accessible for shipping and oil and gas exploration. Companies are more likely to try to drill for oil and natural gas in the Beaufort and Chukchi seas (which, in turn, raises the risk of oil spills).
Less sea ice also exposes coastal communities to heavier waves from storms — increasing the risk of erosion.
The disappearance of sea ice also has consequences for certain species. Declining sea ice is associated with smaller polar bears, who have less ice to hunt seals. Walruses also depend on sea ice as a platform for giving birth and nursing — forcing them onto land.
9) Alaska's permafrost is thawing out
Projections for average annual ground temperature at a depth of 3.3 feet over time if emissions of heat-trapping gases continue to grow (higher emissions scenario, A2), and if they are substantially reduced (lower emissions scenario, B1). Blue shades represent areas below freezing at a depth of 3.3 feet, and yellow and red shades represent areas above freezing at that depth, based on the GIPL 1.0 model. (Figure source: Permafrost Lab, Geophysical Institute, University of Alaska Fairbanks).
Alaska is thawing out. Permafrost along the state's coast has already warmed 6°F to 8°F at 3.3 foot depth since the mid-1980s.
That's a big deal if it continues: About 80 percent of Alaska currently sits on frozen permafrost. And about 70 percent of that land is vulnerable to sinking as the state thaws out.
That sinking ground could cost Alaska an extra $3.6 billion to $6.1 billion just to maintain its buildings, pipelines, roads, and airports over the next 20 years. Thawing will also disrupt Alaska's water supplies and sewage systems — particularly in rural areas. Oil and gas exploration could also be hindered.
There's one other crucial aspect of this to watch. Permafrost soils throughout the Arctic (not just in Alaska) contain about twice as much carbon as the entire atmosphere. As those soils thaw, more carbon-dioxide and methane will escape into the air — further warming the planet. While the report doesn't give any hard estimates here, it warns that this effect is likely to increase in the decades ahead.
