In addition to finalizing the Canada Summer Forecast this week, I have been reading parts of the recently released National Climate Assessment report (NCA), which has made all sorts of headlines over the past couple of days.
I will try to cover the key parts of the report over the course of several blog posts during the next couple of weeks since the report is fairly long with different topics.
The last five decades have seen a progressive rise in the Earth’s average surface temperature. Bars show the difference between each decade’s average temperature and the overall average for 1901-2000. (source: NOAA NCDC).
The NCA summarizes the impacts of climate change on the U.S. and also looks at what the future might have in store.
This extensively, reviewed report was put together by a 60 member federal advisory committee with guidance from over 300 experts in the field.
This report includes analyses of impacts on seven U.S. sectors...human health, water, energy, transportation, agriculture, forests and ecosystems.
According to the report, observations unequivocally show that climate is changing and that the warming of the past 50 years is primarily due to human-induced emissions of heat trapping gases.
Key parts of the report
Temperatures in the U.S. have risen an average of 1.3 to 1.9 degrees F. since 1895, with a majority of that increase occurring since 1970. Temperatures are expected to continue to trend upward this century. Because human-induced warming is superimposed on a naturally varying climate, the temperature rise has not been and will not be uniform or smooth across the country or over time.
The graph below shows the U.S. temperature change over the past 22 years (1991-2012) compared to the 1901-1960 average. Image courtesy NOAA/NCDC/CICS-NC.
The chart below shows the observed U.S. trends in heavy precipitation. (figure courtesy of Kunkel et al. 2013)
One measure of heavy precipitation events is a two-day precipitation total that is exceeded on average only once in a 5-year period, also known as the once-in-five-year event. As this extreme precipitation index for 1901-2012 shows above, the occurrence of such events has become much more common in recent decades. Changes are compared to the period 1901-1960, and do not include Alaska or Hawai‘i.
Sea level rise
The combination of thermal expansion (more heat being absorbed by the oceans) and the melting of glaciers and ice sheets are the main contributors to global sea level rise, which is increasing at a higher rate.
Image courtesy of NASA
Global sea level has risen about 8 inches since the late 1800's.
Arctic sea ice
Since the satellite record began in 1978, minimum Arctic sea ice extent (which occurs in early to mid-September) has decreased by more than 40%. This decline is unprecedented in the historical record, and the reduction of ice volume and thickness is even greater. Image courtesy of the National Snow and Ice Data center.
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