From July 2011 the latest climate normals will be for the 30 years from 1981 to 2010. Climate measures for the 1970s has been dropped and the first decade of the 21st century, the hottest on record has been added. This has resulted in both maximum temperatures and minimum temperatures being about 0.5F warmer on average in the new normals. "The climate of the 2000s is about 1.5 degree F warmer than the 1970s, so we would expect the updated 30-year normals to be warmer,” said Thomas R. Karl, L.H.D., National Climate Data Centre director.
Caption: Comparing average temperatures year round, every state experienced warmer temperatures in 1981–2010 compared to 1971–2000. Image by NOAA.
Temperature measurements are gathered from some 7500 stations and precipitation measurements from 8700 stations.
The 1970s was a particularly cool decade. There is some research that Atmospheric nuclear testing stagnated mid 20th century global warming.
Although warmer temperatures can have some benefits for agriculture, they are outweighed by the problems. Higher levels of warming can negatively affect crop growth and nutritional yields with extreme heat likely to severely damage US crop yields particularly in Corn, soybeans and cotton, the largest three crops by production value in the US. Scientists have also found that increasing atmospheric carbon dioxide interferes with plants' ability to convert nitrate into protein resulting in lower nutritional yield.
Warmer temperatures will also allow pests such as the pine bark beetle and wooly adelgid to survive the winter, and extend their range. With a longer growing season some insects will produce more generations in a single season, greatly increasing their populations. As plants grown in higher carbon dioxide conditions tend to be less nutritious, so insects must eat more to meet their protein requirements, causing greater destruction to crops.
With increased temperatures, the hydrological cycle will be more active which means more extreme weather events such as heavy downpours, tornados, floods, extreme heatwaves, droughts, and bushfires of greater scale and intensity.
We have already seen extensive flooding in the US midwest including Missouri River floods threatening nuclear power plants. The flood threat is forecast by NOAA to continue through summer with more rain predicted and rising temperatures in the Rockies melting the snowpack. "The sponge is fully saturated – there is nowhere for any additional water to go," said Jack Hayes, Ph.D., director of NOAA’s National Weather Service. "While unusual for this time of year, all signs point to the flood threat continuing through summer."
The changing climate in the US southwest has exacerbated drought conditions and wildfires of greater scale and intensity. This season has already seen more than 1 million acres of Texas plains and forests burnt. A 2009 study in Science and reported on in Scientific American found that a warmer climate means more fires which release more greenhouse gases. Bruce Hungate, professor of Biology at Northern Arizona University reported on a fire and climate change feedback loop where Wildfires release nitrous oxide, a greenhouse gas 300 times stronger than CO2, which further contribues to global warming.
A 2009 scientific assessment by the United States Global Change Research Program found that:
* Global warming is unequivocal and primarily human-induced.
* Climate changes are underway in the United States and are projected to grow.
* Widespread climate-related impacts are occurring now and are expected to increase.
* Climate change will stress water resources.
* Crop and livestock production will be increasingly challenged.
* Coastal areas are at increasing risk from sea-level rise and storm surge.
* Threats to human health will increase.
* Climate change will interact with many social and environmental stresses.
* Thresholds will be crossed, leading to large changes in climate and ecosystems.
* Future climate change and its impacts depend on choices made today.
Sources:
* NASA, July 6, 2011 - U.S. Climate: The New Normal
* NOAA - NOAA's 1981-2010 Climate Normals
* NOAA media release June 29, 2011 - Average U.S. temperature increases by 0.5 degrees F
* Living on Earth, June 17, 2011 - interview with Professor Bruce Hurngate on The Fire and Climate Change Feedback Loop
* United States Global Change Research Program - Global Climate Change Impacts in the US (2009) - Key findings, Agriculture
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