A
number of people have been asking me during this exceptional heat wave if it
was being caused by global warming. My
response has been that “global warming doesn’t cause the heat wave; it causes
the heat wave to be hotter.” Privately I
had been telling people that we would likely break the all-time record high
temperature in Columbia in the next 20 years.
That was two years before it happened.
The
fact that so many record high temperatures are being broken is no
surprise. A 2009 study published in the Geophysical Research Letters
showed that daily record-high temperatures were outpacing daily record lows by
a 2:1 ratio in the first decade of this century. If the climate were not warming the ratio
would be 1:1. The study showed that on a business as usual scenario the ratio would expand to 20:1 by 2050 and 50:1 by 2100.
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| The ratio of high to low temperature records from the 2009 study listed above. Click on the graphic for a high-definition view of the graph. Image Credit: Climate Central. |
However,
this year the ratio has expanded to 7:1 for the nation since the beginning of
the year. Almost 8,000 high temperature
records have been set in just the past month.
Some of these records recently have been all-time record highs breaking
records from the Dust Bowl Era. Keep in
mind that there have been two record heat events already this year. The first was the record warm spell in March
and now the exceptional heat wave this past month.
 |
| The ratio of high to low temperature records for June and the first half of 2012. Click on the graphic for a larger view. Image Credit: Climate Central. |
So
how does global warming increase the odds of extreme heat?
If
you have ever played with dice, you know something about odds. The odds of rolling “snake eyes” are one in
thirty six. Those are about the odds of
experiencing a temperature of 101 degrees F or higher in Columbia, South
Carolina. So you would expect to see
that temperature about 3 times a summer.
Obviously, this does not happen every year. There have been summers with no 100-degree
temperatures and the record is 16 101-degree days which was in 1954.
 |
| 2010 |
 |
| 2040 |
A
review of the database shows that the odds were about two days per summer prior
to 1950. The heat waves of the 1950s
changed that on a climatological basis.
Recently the 30-year moving average pushed this to four days per summer
and that is the norm now in 2012.
 | ||
| 2070 |
As
heat-trapping pollution is dumped into the atmosphere it is like loading the
dice to get an extra one. An ensemble of
climate models project that, on our current rate of greenhouse gas emissions,
the odds will be one-in-ten by 2040.
This would mean that on average we could expect to see ten days per
summer with temperatures of 101 degrees F or higher versus the three now.
Last
summer was the hottest summer on record.
It also saw eleven days of 101-degrees+ to rank number 2 in that
category. Last summer was exceptional by
today’s standards, but could be normal in roughly 30 years.
It
does not stop there. The models project that
by 2070 the odds for a 101-degree day in the summer would be one-in-four. It would mean that on average you could
expect 23 days to be 101 degrees or higher.
That has never happened in 125 years of record keeping, yet this would
be the norm. One could foresee a summer
with temperatures topping 100 degrees each day given the natural variability.
The
picture for 2040 is almost cast in stone.
The momentum in the climate system means that anything we do today will
not show up for about 25 years. At this
point very little is being done or planned, so I do not think the picture for
2040 will change. However, we can still
do a lot to change the picture for 2070, but we have to start now.
Drastic
reductions in the emission of heat-trapping pollution are required. The longer it takes, the harder it will
be. Some politicians say we can simply
adapt. We are not doing well in that
category, so far. For many the
adaptation of the future will be to suffer, then die. Is this the legacy we want to pass on to our
children and grandchildren? This is why
some climate scientists like James Hansen have become activists.
I
predict that the new all-time record high temperature of 109 F in Columbia set
on Friday, June 29, and tied the next day, will be broken in the next 30 years. Furthermore, the state record of 113 F was
set at the campus of the University of South Carolina in Columbia and it
Johnston, South Carolina. This will
likely be broken as well.
Two
related videos (which require Flash to view):
Global Warming and Heat Waves (about 1 minute)
Raw interview with James Hansen 2008 (about 20 minutes)
