Guest Post by Willis Eschenbach [Updated, see end of article]
One of the claimed dangers of a few degrees warming of the Earth is increasing drought. Drought is a very difficult thing to fight, because it is hard to manufacture water. So this is a frightening possibility.
I have long claimed that “a warmer world is a wetter world”. I have said this without any actual data, based solely on the following logic.:
Increased temperature —> increased evaporation —> increased precipitation.
Today I graphed the numbers for the US precipitation. I used the USHCN state-by-state precipitation database, which also includes area-averaged values for regions of the US, and for the US itself.
First, here is the change in precipitation in the US since 1895:
Figure 1. Annual precipitation in the US. PHOTO SOURCE
Since the both the US and the globe have warmed since 1895 it seems that a warmer US is a wetter US. However, precipitation is spotty and unevenly distributed. One area can be very wet while a nearby area is dry, so what about the precipitation in each of the states?
The USHCN database contains state data. Since there are drier states and wetter states, I looked at the percentage increase in precipitation rather than the absolute change in precipitation. Here are the state-by-state results:
Figure 2. State by state changes in precipitation, 1895-2009. Values are change per century divided by average annual rainfall.
One of the things that AGW supporters have been saying would result from warming is that the desert belts would move poleward. These are the great belts that circle the earth at about 30° North and 30° South latitude. The North American belt encompasses the Southwestern US (Southern California, Arizona, New Mexico, and Texas) and Northern Mexico. If these belts were actually moving poleward as the globe warmed over the last century, we should see decreased precipitation in the Southwestern US.
Instead, all of the southwestern states have increased rainfall. The main area with decreased rainfall encompasses the Rocky Mountain states in the central Northwestern US.
My conclusions? Precipitation is indeed spotty. A warmer US is indeed a wetter US. And there is no decrease in the Southwestern US data which would show that the great northern desert belt is moving polewards. So either the desert belt is not moving poleward, or the movement is offset by the overall increase in precipitation.
[UPDATE] Some commenters have correctly pointed out that I have only shown the precipitation, which doesn’t show the change in droughts. This is because droughts are a combination of soil moisture, temperature, rain, and other factors. This is measured by the Palmer Drought Severity Index (PDSI). The PDSI index values have the following meaning:
-4.0 to less (Extreme Drought)
-3.0 to -3.9 (Severe Drought)
-2.0 to -2.9 (Moderate Drought)
-1.9 to +1.9 (Near Normal)
+2.0 to +2.9 (Unusual Moist Spell)
+3.0 to +3.9 (Very Moist Spell)
+4.0 to above (Extremely Moist)
I used the USHCN database cited above to look at the state-by-state trends per century in the PDSI. Note that these are not the average PDSI values by state, which are without exception in the range -1.9 to +1.9 (near normal). Figure 3 is a histogram of the trends per century. A “histogram” shows the number of states (left scale) that have a certain trend range (bottom scale).
Figure 3. Histogram of state trends per century of the PDSI
The trend in most of the states (39 out of 48) is toward less drought (increasing PDSI). However, most of the trends (32 of 48) are between 0 and +2.0, which is not a large change. As a result, most of the trends are not statistically significant. Figure 4 shows the significant state trends:
Figure 4. Significant trends in the PDSI in the US states.
As you can see, despite the warming of the last 115 years shown in the USHCN dataset, while some of the PDSI trends have decreased, almost all of the statistically significant changes in the PDSI are positive (less drought). And few of the changes are statistically significant.
The IPCC models say that increasing warmth will lead to increasing drought, particularly in the mid-latitudes:
In a warmer future climate, most Atmosphere-Ocean General Circulation Models project increased summer dryness and winter wetness in most parts of the northern middle and high latitudes. Summer dryness indicates a greater risk of drought.
Despite these model prediction, we have seen no such increase in drought in the US. For most of the US, there has been so statistically significant change in the PDSI index showing the number and strength of droughts in most US states. And where there has been a statistically significant change, it is in the direction of reduced drought.
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This is a simple question but has a very complex answer. The distribution of moisture over geographic areas has many factors, few that respect political boundaries. Gross measurements like average rainfall or average temperature may make nice maps but in essence tell us little about what is happening in large geographic areas. Wyoming the Dakotas and Nebraska are good examples. Physiographic regions are a much better way to look at these things. Now the data sets may not exist for a solid physiographic region by region analysis. As others have pointed out form, timing, intensity and so on are all factors that need to be considered. That said, this is a very interesting presentation. I think the take home message is you can’t predict or model forward what you don’t understand.
Someone asked if climatologists have ever read any geology or something to that effect. It has been clear to his geologist, since I was a small boy growing up in Wisconsin, they do not, have not and even if they did, probably don’t understand it. Another big knowledge gap lay in soil science. From what my pedological associates tell me they are even more ignorant of that science.
In the early 80’s I planned and excited an extensive drilling program in central Alberta, west of Edmonton. Knowing from local rainfall records (±15 years) that June was by far the wettest month of the year and knowing I was to work mostly on highly bentonitic soils, I choose July to start. That year June was mostly dry and warm. July was very wet. It was quite a scrabble to get things finished on time.
Earth also had less deserts during other periods when earth was warmer. Growing deserts usually tend to coincidence with global cooling. Norwegian weather stations also shows increase in precipitation during modern “global warming” period: http://eklima.met.no/yr/trend/RRA_G0_Year_650_NO.jpg
During this years unusually cold winter we also had the driest months in over 100 years in some areas of this country.
The preciptiation trends for winter for all of norway: http://eklima.met.no/yr/trend/RRA_G0_Season_650_NO.jpg
sphaerica (04:44:07)
Yeah, I know, sphaerica. Which is why I looked at the data … and found out perhaps it wasn’t that simplistic after all.
Gosh, you mean that the climate actually changes, and that rainfall patterns will change as well? Why didn’t someone warn us in 1895?
Also, you say “more of that added precipitation will quickly be lost again by evaporation”. While some precipitation is always lost to evaporation, more rain never means less water in the ground. It means more water in the ground, despite increased evaporation.
Actually, the USHCN data claims that 1895-2009 the temperature rose 0.8°C … however, I’m glad to see you describe that as “minimal”. On the other hand, I’m not so happy to see your claim that we are “committed … to at least 1.5C warming.” What is your citation for that claim?
You mean water can cause flooding? Who would have guessed? And things are going to change? Say it isn’t so!
sphaerica, if it looks like it is going to get drier, AGW folks go “Oh noes, here comes the droughts”. And if it looks like it is going to get wetter, its “Oh noes, here come the floods” … dude, weather changes. Better get used to it, because it’s not going to stop. Given my choice, I’d vote for more rather than less rain, perhaps because I grew up on a cattle ranch and I’ve seen what both too little and too much water can do. YMMV.
Ya know, sphaerica, this question of the Southwest is one of the reasons why I did this study. Having lived in the Southwest at times, I wanted to see if the predictions of a dryer Southwest in a warming world were actually true. Turns out the USHCN data doesn’t support that prediction, the Southwest got wetter rather than dryer when the US warmed 0.8C.
However, the actual data not supporting your argument doesn’t stop you or even slow you down, here you are again predicting doom for the Southwest … sometimes I wonder why I bother.
stevengoddard (06:10:56)–
With that shade of pink, Montana has either gone commie or it has trended drier as we discussed in your post about glaciers.
Chris Riley (08:49:01)
Any discussion that attempts to infer a link between increases in CO2 and decreases in the food supply as a result of (computer projections of) drought, that does not take into account the positive externalities of CO2 emissions is simply not science. It is propaganda
Not forgetting that GREEN COLOR is the color we humans can best perceive best. Curious isn´t it?
Green wavelength=560–490 nm
Most probably the color The Prophet best perceives is the INFRARED (700 nm to 1mm). (Usually the devils´preferred color)
MattB (05:00:48)
MattB, given CSIRO’s pathetic record in even describing the rainfall in Australia, I might concur. Plus I could use the money.
Seriously, if you’re an Aussie, you should call them to task for their repeated and egregious misrepresentations regarding climate.
Or you could just believe them, I suppose …
Hmm I just realised that comment may strike many of you as sarcastic. It’s not.
PS – what exactly did I “disprove”?
pwl (05:14:17)
Thanks, fixed.
Rhys Jaggar (05:51:18)
Haven’t a clue, Rhys. The USHCN data only goes back to 1895.
Willis, more good stuff!
Could you do the same thing with humidity?
– and baro pressure?
– and also windspeed?
And, as a grand finale … if you show a graph of all four with temperature, we ought then to see what has happened to the US CLIMATE over the last 100 years …
( I assume that it is permissible to talk about the US having a ‘climate’ as opposed to just lots of ‘weather’ …)
Anybody else tried to make sense of sphaerica’s point?
” …. water doesn’t evaporate and then precipitate in the same place, ………”
Try living in the Tropics …
Chris Riley (08:49:01) :
“The science of Botany was well developed long before the politicization of climate science.”
… and it goes on developing, refining the questions and getting better
answers. You see, going from short-term experiments at leaf level to
long term experiments on whole canopies, extrapolating to regions and
…. the bets on this mechanism actually being significant is quite open.
For instance: The interaction of rising CO2 and temperatures with
water use efficiency. Eamus 2006. Plant, Cell & Environment
Volume 14 Issue 8, Pages 843 – 852
supercritical (10:46:20),
Interesting point about the U.S. climate. From my handy electronic dictionary:
Continuing their sloppy science by using inaccurate language, GISS, CRU and just about everyone else on the peer review gravy train use the term “climate” when referring to the overall global temperature.
It’s probably too late to change its recent widespread misuse, but the term climate, when referring to the entire globe from the poles to the equator, is more of a ‘climate catastrophe’ than the current condition of the planet, which is well within its normal range and actually quite benign.
The majority of sand deserts on Earth are caused by humans, especially by goat herders.
sphaerica (04:44:07)
sphaerica, regarding your claim that there is heat “in the pipeline” as they say, see Dr. Pielke Senior’s posts here and here, and also the posts that he cites. It’s a good overview of the question.
sphaerica (04:44:07)
{The fact is, at the moment the amount of warming that has been seen is minimal, because the planet doesn’t warm instantly, but the CO2 in the atmosphere now has already committed us to at least 1.5C warming, where we’ve only seen 0.5C to date}
can you elaborate on this statement please. It just does not come clear in my brain. 🙂
Willis Eschenbach (11:14:23) :
sphaerica (04:44:07)
… The fact is, at the moment the amount of warming that has been seen is minimal, because the planet doesn’t warm instantly, but the CO2 in the atmosphere now has already committed us to at least 1.5C warming, where we’ve only seen 0.5C to date. …
Interesting as your map of USA precipitation 1895-2009 is can you tell
your readers please, that it does not disprove IPCC projections showing a South West USA dustbowl towards the end of 21th century.
You might want to extend your analysis to global data. There are definitely areas that have dried over the past century:
http://www.cgd.ucar.edu/cas/adai/papers/Dai_pdsi_paper.pdf
(PDSI=Palmer Drought Severity index)
And surface warming has caused a good portion of the more recent drying, along with El Nino and precipitation changes.
So, yes droughts have been and will continue to be problematic as the world warms, despite the wetting of the US region.
@ur momisugly guidoLaMoto (04:02:05) :
“The positioning of deserts has little to do with temperature, but mostly with geography: they form around 30deg N & S latitude due to Hadley Cell Circulation, and usually on the leeward side of mountain ranges.”
That seems quite logical but forgive me for asking a question that might reveal my ignorance. What happened to the Sahara? Parts of North Africa used to be greener. Libya and Egypt have often been called “the granary of the Roman Empire.” When I was at school a common explanation of why they turned to desert was that goats ate all the vegetation. If goats really did turn the Sahara into desert then presumably manking could have just as devastating effect on our planet.
Thanks to this blog I have become a lot more sceptical of claims of man-made global warming but the example of the Sahara is a rather worrying one.
Doug in Seattle (09:46:53) :
excellent observations. Both about Anazazi and the North Africa. There was an article ( not sure if it was national Geographic, but might have been ) That shows the extensive Aqueducts in Old Carthage Area, that shows there was enough rains in the mountains that they could cultivate large fields. It was warmer then than now.
mikael pihlström
” the bets on this mechanism actually being significant is quite open.”
This is as it should be, but for practical purposes, isn’t. As presented by the MSM, and even most skeptical politicians, (to paraphrase) “the science is settled and there are no positive components to the externality involved in the burning of carbon worth mentioning, much less measuring or accounting for. Exposure to these popular sources of information would lead a rational disinterested observer to conclude that the negative externality must be three or four orders of magnitude larger than the sum of all positive effects of increased CO2
My point was that research that occurred prior to the politicization of this is much less likely to to have been influenced by politically motivated financing. Newer publications should not be given an automatic presumption of superiority, particularly when only the newer research was released after the issue became politicized. Both proponent and skeptical scientists are human and cannot be assumed to be immune to the personal-financial and personal-social consequences of the results they report.
This is not meant to be a criticism of Eamus. I will read his paper. I will say that I will look harder at the “extrapolations” you mentioned than I would if the paper came out in 1986 rather than 2006.
Since I’ve been interested in historical and paleo climate events related to our evolution and migration across the globe it seems to me to paraphrase our experience … ‘colder is drier’. This does not make the corollary true and with our geographical expansion you really are subject to local conditions. In my geographic area La Nina’s generally make it colder with more precipitation but it is highly variable. There have been dry, cold La Nina years.
This past winter was welcome on the Northern Great Plains, but I expect and fear cold is coming of the scale Bastardi is describing in his crystal ball.
http://www.accuweather.com/world-bastardi-europe-blog.asp?partner=accuweather
If you read the IPCC AR4 peleo section it does indeed state that a warmer world is a wetter world. It is known fact to geologists etc….
The IPCC AR4 body also discuss the effects of AGW on water supply and states a net benefit, though some areas may experiance more arid conditions. This is unfortunetly taken out of context in the SPM where it states more droughts are forecast. The whole “drought” claim seems to be something taken out of context which the scientists failed to correct.
I also recall that the climate models used for AR3 didnt have volume balance checks which resulted in them loosing water over time plus they also underestimated evaporation / evapotranspiration rates by 3x over land. Seems the models had some very basic issues, this could have led to earlier claims of drought. The AR4 models now apply volume balance checks I believe (its modelling 101 to include volume balance checks!). I recall there was a paper published on this but I dont have it to hand.
As someone who works modelling the hydrological cycle, its clear warming will increase evaporation / evapotranspiration, if the sea warms, evaporation will increase and the hydrological cycle will intensify. I am not sure how well they modell this, but as the hydrological cycle increases, it forms more of a cooling effect to counter the warmth. If the earth warms 1 degree than theoretically the atmosphere can hold an additional 8% moisture, which increases the rainfall potential. However, I live in an area that would suffer more droughts, but thats because rainfall here is determined by the mountains and the predominant wind direction. During the 1940’s warm period we had dry weather and the 1970 cool period gave us more rain and heavier rain.
Lush Vegetation Brings Locusts to Eastern Australia, courtesy from our good friends http://earthobservatory.nasa.gov/IOTD/view.php?id=43673
“mikael pihlström (11:47:28) :
[…]
Interesting as your map of USA precipitation 1895-2009 is can you tell
your readers please, that it does not disprove IPCC projections showing a South West USA dustbowl towards the end of 21th century.”
I see the word “Disprove” occur every time a pro-AGW person writes something. Please explain how one can disprove something that has never been proven, in this case the assumption that a dustbowl will occur (the fact that some model runs indicate so is not a proof.).
Only because you think the AGW modelers have proven something doesn’t make it so. They have not even correctly projected the temperatures of the last 10 years – and they have never predicted anything because a prediction would be verifiable.
The whole business of the pro-AGW people is making wild guesses and then saying: “Now disprove the things that i have just said.”
This brings out a bit of my speculative brain, for what it is worth. Not all of the below ideas fit together, necessarily, but some may be pieces of the larger puzzle.
Disclaimer for any warmers who might show up: This below is all weather anecdotes, with only a light suggestion of being climatic. I do know the difference between weather and climate, though I know it less than most who visit this site. But the particulars are worth noting, I think.
1. At least eastern SD was involved in both huge Mississippi River floods, the 1993 one and the other, which was around 2005 or so. Those rain systems stalled over Iowa, pretty much, so SD was in the system rotation not far from the eye.
2. I lived in Denver and know that the rain clouds that form in the Rockies behind the front range tend to dump their rain in the mid-afternoon east of the foothills. I assumed this was because a certain amount of convection/heat and time were needed in order for the clouds to get over the last range. If something like this occurs farther north, where the mountains are somewhat lower, perhaps the lesser altitude and its commensurate warmer temperatures means the rains hold out and fall farther from the mountains.
3. I’ve lived the last 35 years around Chicago and observed that collisions of the warm Gulf air masses with the cooler dry continental air masses along a line that is generally from about San Antonio/Dallas to Madison, WI. These colliding air masses are what precipitate the tornadoes in central and eastern OK, KS and TX, and bleed into MO, IA and IL. This impacts me in the NW Chicago suburbs pretty often, where we are right on the edge and I’d hate to have to predict which way things are going to break. But this is just the general pattern. Depending on the strength of each air mass, it seems that the front shifts eastward or westward. Eastern SD is on the western edge of this activity, so if I am not mistaken, this is where the rainfall is greatest within the state and what makes it different from the other Great Plains states.
4. There are times when the latter pattern has such a strong SSW wind pattern (with its warm gulf air), that the system from the west simply can’t move it, which causes the stalling and the great 100-year floods.
(Just a note about these stalled systems: I recall in September 1986 driving south down the length of IL to Carbondale and a boat race. The pattern had stalled for weeks, and the flooding in the Chicago area was the greatest in memory. As I drove, the clouds were consistently moving across the sky from SSW to NNE at a rate I’ve never seen before or since, not for a huge system like it was. The dividing line turned out to be about 20 miles north of Carbondale. The air mass north of that had huge amounts of water and was very cool – around 50F or so. As I approached the edge of the system, the clouds were still making for a bat out of hell for the NNE, and then within a few hundred yards the sky became clear and warm, in the mid-70s. This pattern had lasted about 2 weeks straight, stalled and dumping all its water in narrow bands.)
I suggest that eastern SD gets some of these stalled system effects from time to time, often enough to make it unique in the general area. And I suggest further that the warming since 1895 means stronger warm air masses coming off of the Gulf of Mexico.
Combining these four anecdotal observations, it seems like SD is just far enough east of the mountains and just far enough north for the precipitation to fall there preferentially.
Chris Riley (12:19:27) :
“Both proponent and skeptical scientists are human and cannot be assumed to be immune to the personal-financial and personal-social consequences of the results they report”.
“This is not meant to be a criticism of Eamus. I will read his paper. I will say that I will look harder at the “extrapolations” you mentioned than I would if the paper came out in 1986 rather than 2006.”
Fair enough. I was always also not saying that the older paper you
cited was flawed in any way. It was just about another research question.
I don’t believe in the financial motives etc, but sure, science has its sociology
and we have to be sceptic about enthusiasm.
sociological