Are the current extreme weather trends in the USA indicative of global warming?

Question

I'll be the first to tell you that an individual weather event doesn't tell you anything about global warming. However, look at all the extreme weather trends we're seeing in the US right now:

A huge drought in the southeastern states, along with droughts in the southwest and northwest:

http://www.drought.unl.edu/dm/monitor.html

The drought in the southwestern states which has already lasted 10 years is expected to last for 90 more:

http://www.livescience.com/environment/070405_southwest_drought.html

Increased numbers of severe wildfires in the western states, most recently the San Diego wildfires:

http://www.ktvu.com/globalwarming/10309740/detail.html

Taken all together, could these extreme weather events be indicative of global warming?

Bob - the increased wildfire statistics were over the past several decades.

Answer 1

Dana, what we need here are some numbers, more specifically Return Periods. This is the value assigned to anomalous events and expresses them as a probability measure in years, thus an event with a RP of 500 is one that would ordinarily be expected to occur once every 500 years. RP is sometimes called Recurrence Interval.

If you can find out the RP's of these events it would provide a good indication as to whether GW was a factor or not, quite often media reports include RP's (they do in the UK at least).

A bit of caution is needed. There are so many adverse weather eventualities that in any one year it's normal to experience some anomalous events. Where it starts becoming un-natural is when the combined propabilities start running into their thousands or millions.

I'll give you an example from the UK. A few months ago we had the worst flooding for a long time, it had a RP of 400, that in itself isn't particularly unusual but less than a month later we had even worse flooding with a RP of 1000. The odds of both such events occurring in the same year - 1:400,000 the odds of them being in the same month 1:4,800,000. Quote clearly not natural. Factor in all the other floods in the last few years, the droughts, heatwaves, hurricanes, tornadoes, record breaking temps etc and the odds become a staggering 1 in 13 billion.

I'm not keyed up on normal weather patterns in the US but it certainly seems that something unusual is going on.

Increased droughts and wildfires are a consequence of global warming and if there has been an abnormally high number of such events over a prolonged period of time then it's probable that GW is a contributory factor.

We know that the world is warming up and we know that humans are a part of the cause, it would be foolish to claim otherwise. Similarly, we know many of the consequences of global warming. Even a very small increase in temperatures has an effect on the weather; in climatological terms we've seen a very significant increase in temps and undoubtedly this has, is and will affect the weather.

Without knowing more it's difficult to say with any degree of accuracy just how much GW is contributing to current events over there in the US but I think it would be a safe bet to say that GW has contributed to the wildfires and is very likely to be a factor in the prolonged drought you mention and the extreme temps that many people are experiencing.

If poss, try and find those RP values, they could be the best indicator you'll find that GW is or isn't involved.

Answer 2

Wow!Everyone frames extremes from the time they were born. Let's forget about the dust bowl days when dust storms started on the Canadian border and swept south to form dust storms thousands of feet high over the plain states.

Let's forget about the associated drought with these years that helped usher in a national depression. We weren't born then, so as far as we're concerned these things just didn't happen.

Fire? They must be caused by global warming. After all, it couldn't be poor forest management. That wouldn't fit our premise, so forget it.

The southeast experiences droughts about every 12 years. No big deal. The rains come back. By spring or next year no one will ever remember this drought except some who live there. Yea, this is the lowest the lakes are in the last 100 years. No one tells you that there are no natural lakes in the south. All the natural lakes in the north were caused by receding glaciers. All southern lakes are only about 50 years old. And the main reason for them being low is because the water is let out to protect a fish in Florida, not because of natural conditions.

Answer 3

So once again the drought in the Southeast is caused by global warming. I don't believe so. The reasoning is La Nina which has been around for millions of years I'm sure. You can expect the drought to continue through the winter due to La Nina.

Answer 4

No, there have always been extremes. There have always been droughts. The number of wildfires will increase due primarily to horrible management practices and the interference in natural cycles of fire. I live in Southern California and it is a very dry place normally. The current La Nina is expected to continue the drought. La Ninas have been around before history. This is caused by ocean temperatures off Peru LOWER than normal for a period of greater than 5 months. Everything bad in the world does not result from global warming. Warmth can sometimes be and usually is beneficial.

Answer 5

No different than any other periods in history. Drought in the 1930s. Floods in the 1950s. The famous winter of 1894 where no lakes froze south of southern Canada (that's what jump-started the refrigeration industry). The freezing winters of the Revolutionary war. The numerous hurricanes of 1615. The little ice age. The medieval warming period. The drought that caused the Anasazi Indians to abandon Canyon de Chelle.

Nothing new under the sun.

The current wild fires are a result of years of fire suppression.

Answer 6

Indicative is the right word. I hope there is not too much running around blaming global warming, it would kind of undermine all that scientific work.

With the floods in the UK this year, the government's chief scientific officer said the floods were a once in a 50 year floods, not caused by global warming, but were more serious due to the extra moisture in the atmosphere due to global warming.

I hope one of your guys can come up with something equally sensible.

Answer 7

Al Gore would say Global Warming contributed!!!

Answer 8

No, except maybe the very long running southwestern drought. Everything else you cite is focused on this year.

One year doesn't mean _anything_ in this business. To the extent your question, even if it's being misinterpreted, encourages looking at short term events in one location, it's a really really bad idea.

The only way to know anything about global warming is to look at global trends over many years.

I know you understand that, but this question could encourage some people to go wrong. The phrase "look at the extreme weather trends we're seeing in the US right now" is particularly egregious.

Bottom line: Boo.

Answer 9

The wildfires most certainly are not associated with global warming, if they were, the fires in San Diego should have been worse in the 80's.

http://data.giss.nasa.gov/cgi-bin/gistemp/gistemp_station.py?id=425722900004&data_set=1&num_neighbors=1

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Answer 10

When an unusual weather event happens and people retrospectivly try to work it into their understanding of global warming, it's really not convincing. By definition, unusual events will happen from time to time and temperature generally doesn't coincide with precipitation.