Weatherdem's Weblog

Bridging climate science, citizens, and policy

U.S. Record High Temperatures Recorded At Twice The Rate Of Record Lows This Decade

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A news release was issued last Thursday that I flat out missed, which was unfortunate (though I’m glad I eventually found out about it).  A study (submitted to Geophysical Research Letters for publication) was conducted by climate scientists at the National Center for Atmospheric Research (NCAR) in Boulder, CO, Climate Central in Princeton, NJ, the Weather Channel, and the National Climate Data Center in Asheville, NC.  They examined trends in record high temperatures and record low temperatures over the past 6 decades, through 2006.  What they found isn’t terribly surprising: the ratio of record highs to record lows became unbalanced in the 2000s.  There were twice as many record highs as record lows across the continental United States.  That’s an increase from 1.36:1 for the 1990s and 1.14:1 for the 1980s.  Climate change is affecting us today.  Not tomorrow, not later this century.  Today.

With retrospective data results in hand, they ran climate models with different greenhouse gas emissions scenarios and  through the 21st century to see how the trend developed.  They used an A1B emission scenario, which is a slightly above average emissions and warming scenario type that was tested in the IPCC’s 4AR.  Here is a graph (source) that puts the A1B scenario in context with other scenarios and 20th century surface warming:

The left part of the graph shows model averages as thick lines and the +/-1 standard deviation from that mean for 3 scenarios.  The right part of the graph (with the vertical bars) shows the best estimate as a solid line and the likely range assessed for six scenarios.  The A2 and A1F1 scenarios are the really scary ones.  I’ll take this opportunity to again point out that our current emissions (per real-world observations) trend is matching these scenarios.  Keep in mind that this means we’re well on our way to exceed the A1B model results unless we take concerted action within the next couple of years.

By 2050, the ratio of record high temperature records to low temperature records over the continental U.S. grows from 2:1 to 20:1.  By 2100, the ratio grows to 50:1.  In the context of climate change, this means far fewer record lows are likely to be observed under a mid-range warming scenario.  Nightly lows across the country will steadily get warmer and warmer.  These results are more optimistic in nature, but still in general agreement with recent findings that temperatures across the internal U.S. could reach 15°F to 18°F.  I think it’s easy to conclude that the 20:1 and 50:1 ratios are generous estimates.

The A1B scenario underestimates a number of processes and it is widely acknowledged that it ignores some important other processes (i.e. ice-related) due to lack of physical understanding.  Research is being conducted on those processes to draw them into the fold.  Indeed, modeling centers are already running simulations that will be used for the IPCC 5th Assessment Report a few years from now.  Some of the weaknesses in the 4AR will be lessened, others will remain.

But the trend found through the end of the 20th century and the very beginning of the 21st will undoubtedly continue for some time, even if we take action soon.  Warming has continued this decade, contrary to what the deniers would have you believe.

Cross-posted at SquareState.

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