Friday, August 3, 2018

Contrasting Heat Waves: July 1960 vs. 2018

Motivated by an intriguing tweet by University of East Anglia Professor Tim Osborn, I thought we would compare global temperatures for July of 1960, which was the warmest 20th century July at the Salt Lake City International Airport to July of 2018, which was the 5th warmest on record and also feature remarkable temperatures in many regions across the Northern Hemisphere. 

The graph below illustrates the anomalous warmth of July 1960 as well as the recent string of very warm Julys in the 21st century. 

Source: NOAA Regional Climate Centers
For convenience, I am going to examine the surface temperature departure (or anomaly) from the 1981-2010 average from the NCEP/NCAR reanalysis for the two Julys.  There are better datasets for doing a surface temperature comparison, but the differences are not going to be all that significant.

In July 1960, anomalous warmth covered much of the western continental U.S. and southwest Canada, with the most anomalous temperatures along the US-Canadian border.  Elswhere, one sees a mixture of both cold and warm anomalies with Most of southern and central Europe and central Asia being cold and far northern Europe warm.  By eye, it appears that overall the Northern Hemisphere is probably a bit cooler than the 1981-2010 climo, which is what we would expect given the global scale warming that has occurred since 1960.

In July 2018, we see a different story.  Not surprisingly, anomalous warmth exists over the western U.S., but not the dominance of warm anomalies elsewhere, including maxima in Scandanavia, North Africa, and central Asia.  Cold anomalies are more localized.  

This is consistent with the warming that has occurred in recent decades, which has stacked the deck for warmth, so that longer, more severe heat waves are more likely.  

Tim Osborne's tweet went a step further than my simple analysis, however.  He compared the 1976 and 2018 heatwaves in the UK (relative to the 1960-1990 average, which is 20 years sooner than the plots above), but then examined what would happen based on climate projections for 2070 and scenarios in which greenhouse gas emissions peak in 2080 (RCP6.0) or are aggressively reduced to limit the global average temperatures to less than 2˚C above preindustrial.  In either case, we have more warming in the pipeline and are facing a hotter future with longer, more severe heat waves.  How much hotter depends on future greenhouse gas emissions.  

Source: @TimOsbornClim (
This is why "Normal Is Gone Forever".  The future climate is dramatically different from the one you grew up with.  

It should be noted, however, that the emergence of climate shifts depends on the variable.  Detectable and significant shifts in temperature are early "emergers".  Shifts in other variables, like snowfall and snowpack are occurring, but may emerge more slowly in some regions compared to others (e.g., declines in snowfall and snowpack may occur later or more slowly in colder regions than warmer regions).  For more discussion of this, see our August 2013 posts Western Snow Trends and Global Warming Part I and Part II.

1 comment:

  1. I feel it is always important to segregate local causes of increased temperature from regional, continental and global warming causes. Clear segregation of those factors generating increased local temperatures prevents increasingly marginalized climate deniers from claiming that global warming is the result of agenda driven climate scientists. With respect to increased local Salt Lake City overnight temperatures, much of those increases might be attributed to local development patterns. In the 1960s there were probably less than a hundred thousand registered vehicles in Salt Lake County; currently there are over 500,000. I read somewhere that each automobile generates the equivalent of a 60000 watt space heater. Running 500,000 space heaters in the Salt Lake Valley a few hours each day presumably would affect local temperatures. Similarly, I guesstimate that perhaps the percentage of paved over or rooftop surfaces in Salt Lake County has reached between 25% and 40%. Such development patterns could easily explain our local experience of increasing overnight urban temperatures. They do not explain the continental and global increasing temperature patterns that you cite. However, much of the local increases can be attributed to our collective local planning and zoning decisions about how the valley was to grow between 1960 and the present. No governmental planning documents that I am aware of in the Salt Lake Valley during that time ever considered the impact of a local heat island effect from development. We are now reaping the costs of that lack of foresight. Segregating such local and global causes clarifies our collective responsibility for controlling those things that we have direct and immediate local power to change. Thank you for another informative weather in climate blog entry. - Kurt