In VI – Australia CanESM2, CSIRO, Miroc and MRI compared vs history we looked at how each model thought rainfall had changed in Australia over about 100 years, and we compared that to observations. We did this for annual rainfall, also for Australian summer (Dec, Jan, Feb) and Australian winter (Jun, Jul, Aug).
Here we will look at two of the four emissions scenarios. We compare 2081-2100 vs 1979-2005.
Note that we are not comparing the end of the 21st century from the model with observations at the end of the 20th century. That produces much different results – the model’s view of recent history doesn’t match observations very well. We are comparing the model future with the model past. So we are asking the model to say how it sees rainfall changing as a result of different amounts of CO2 being emitted.
The two scenarios are:
- RCP4.5 – with current trends continuing we are something like RCP6. I think of RCP4.5 as being “what we are doing now” but with some substantial reductions in CO2 emissions. But it’s nothing like RCP2.6, which is more “project Greta” where emissions basically stop in a decade
- RCP8.5 – extreme CO2 emissions. Often described as “business as usual” perhaps to get people’s attention. Think – most of Africa moving out of abject poverty, not passing through the demographic transition (so population going very high) and burning coal like crazy with the efficiency of 19th century Europe.
Each pair of graphs is future RCP4.5 as % of recent past, and RCP8.5 as % of recent past. The four models, clockwise from top left – MPI (Germany), Miroc (Japan), CSIRO (Australia) and CAN (Canada):
Figure 1 – Click to expand
And now the same, but only looking at Australian summer, DJF:
Figure 2 – Click to expand
Depending on which model you like, things could be really bad, or really good, or about the same with “climate change”.
Note that the color scale I’m using here is the same as the last article, but different from all the earlier articles, the % range is from 50% to 150% (rather than 0% to 200%).
References
An overview of CMIP5 and the experiment design, Taylor, Stouffer & Meehl, AMS (2012)
GPCP data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/
GPCC data provided from https://psl.noaa.gov/data/gridded/data.gpcc.html
CMIP5 data provided by the portal at https://esgf-data.dkrz.de/search/cmip5-dkrz/
SOD: I appreciate all of the work that went into making these posts. As best I can tell from them, there is little reason to have much confidence in the changes they predict. … which is frustrating without some overall rational or concept that explains what models do well in predicting precipitation and what they do poorly.
The one thought that keeps coming to my mind is that the change in global precipitation is tightly constrained by thermodynamics and probably can’t be much different from a 2% per degK increase. So all future large changes in precipitation are shifts from one location to another. Your plots of absolute change in precipitation accurately convey information about the largest shifts in precipitation, but the % change plots do not. IIRC, the largest precipitation shifts are into the Pacific ITCZ and from areas on either side of the ITCZ. It would be nice to have a rational for this prediction. I’ve reviewed plots for other big shifts, but didn’t retain any concepts.
SOD: I really like this Hovmoller diagram of precipitation from Dai (2005) because it provides a mechanism (or illusion of a mechanism) by which seasonal change effects precipitation: The ITCZ and the attached Hadley cells move north and south with the seasons. If an AOGCM did a good job of reproducing this phenomena in a particular region – say Australia or India – I might be inclined to place more faith in that model’s ability to predict changes in rainfall associated with predicted changes the ITCZ and Hadley cell. During the African humidity period, the same tropical monsoon that currently penetrates north into India (to 30 degN) during the summer (second row of figures) is believed to have penetrated north into the Sahara and Saudi deserts instead of stopping at about 15 degN as it does today (first row of figures). This change in northern extent of the African monsoon about 6000 years ago is believed to be associated with changing orbital mechanics, but AOGCMs fail to predict a green Sahara during the African Humid Period. There is a band of semi-arid land in the NH and SH subtropics where precipitation occurs almost exclusively during the summer and is associated with movement of the ITCZ. The projected precipitation changes in these arid regions might be meaningful if the model did an accurate job of reproducing changes in this transition zone – say in El Nino vs La Nina years or after volcanic eruptions. The failure to predict a green Sahara during the African Humid Period (which was studied as part of CMIP) is a sign that the predictions of change in this region (with large % changes) shouldn’t be considered reliable.
Unfortunately, in temperate regions precipitation is associated with weather fronts that generally move east (or northeast or southeast). IIRC, most of the rain in the eastern half of the US comes from moisture moving northeast (or north) from the Gulf of Mexico. Since storm tracks generally follow undulations in the jet stream, a Hovmoller diagram with latitude on one axis wouldn’t illuminate this mechanism. To some extent, the jet stream is often moving northeasterly in Western US plus southeasterly in the Eastern US OR southeasterly in the Western US and northeasterly in the Eastern US producing distinctively and opposite warmer/cooler and rainy/dry weather. Since the undulations in the jet stream are highly chaotic, I’m skeptical that models have the ability to predict a shift in precipitation from one side of the country to the other. On the other hand, during El Ninos, more storms penetrate the West Coast of the US further south than usual, bringing more snow to the Sierras in California and less to the Cascades in Washington and Oregon
Fig. 3. Zonally averaged precipitation (mm day−1) as a function of latitude (vertical coordinate, negative for the Southern Hemisphere) and month averaged over 1979–99 from (left) observations (CMAP) and (second column from left) one of the better and (right column) worse model simulations, together with the (third column) average of the 18 models. The zonal averaging was done for six longitude sectors (from top to bottom): Africa and Europe (10°–40°E), the Indian Ocean and Asia (60°–110°E), the western Pacific Ocean and Australia (115°–155°E), the central Pacific (165°E–135°W), the eastern Pacific and North America (80°–120°W), and the Atlantic Ocean (15°–40°W).
Frank,
The graphic didn’t show up in your comment (wordpress has some rules on graphics inserted in comments that I don’t understand).
Here it is, from Precipitation Characteristics in Eighteen Coupled Climate Models, Aiguo Dai, AMS (2006):
Click to enlarge
SoD.
If I click on the link in Frank’s comment, it says ‘page not found’. That may be one reason that they didn’t show up. Also, at lucia’s The Blackboard, I think you need author privileges to post images.
DeWitt,
Thanks. You know, I’m sure you figured it out here before.
I have a recollection (from you or someone else that did it) that the graphic needs to be from a wordpress site, and there are a few other graphics sites that wordpress will show graphics from.
SOD: Thanks for posting the Figure. I’ve been reasonably successful getting figures to display in comments recently, but I don’t have a clear understanding of what does and doesn’t work.
SoD, just checked in, interesting series thank you, good to see you back.
Hello – checking out this site – recently recommended to me .. may I ask who is the author and possibly their background? Thanks.
I don’t know and I don’t care. The idea that one needs proper credentials before one can be credible is unfortunate. Why not read some of the posts and comments and see for yourself.
Hope: In today’s world, there can be advantages to remaining anonymous at websites, and big disadvantages if you want credibility. On the other hand, someone can have loads of credentials, but be more interested FOR POLITICAL REASONS in telling you what to THINK about climate science. “In about this blog”, our host tells us:
“Opinions are often interesting and sometimes entertaining. But what do we learn from opinions? It’s more useful to understand the science behind the subject. What is this particular theory built on? How long has theory been “established”? What lines of evidence support this theory? What evidence would falsify this theory? What do opposing theories say?”
Our host takes you on a journey to find answers to such questions and usually provides references with each article. On a journey of exploration, you get to decide what to think, which is why both smart skeptics and supporters of the consensus hung out here. My recently, Professor Dessler has come to explain why his latest paper has the answers.
Hope,
Thanks for your interest. My name is Science O’ Doom, an interesting choice from my parents that I’ve had to suffer my whole life – no, I’m kidding (on the internet there’s always someone who doesn’t get the joke).
The idea of this site, which came to me in a dream (again, that bit, kidding) is to look at climate science critically. That does mean actually reading what climate scientists have written and published (unlike most inappropriately-named “skeptic” blogs).
The motto of possibly the oldest continuing scientific society in the world, the Royal Society, is “take no one’s word”.
It’s not “we believe the science”. And it’s not “we believe the scientists selected by journalists”, which is what “believe the science” actually means in practice.
It means, weigh up the evidence.
So, who I am is irrelevant. The scientific method is to look at the evidence and the arguments.
If someone is Super Distinguished Professor of Climate Science at The Most Prestigious University Ever then maybe you might just want to take their word for it. Me, not so much.
I’m pretty sure most climate scientists would agree with this approach.
I apologize for jumping into a post but I was reading through some of your archives on Gerlich because I’ve been following and occasionally commenting on a climate change discussion on an AIChE discussion board. The gentleman that runs this website (https://www.coatsengineering.com/Sustainability_and_CO2.htm) is spouting out his argument against the “mass conspiracy theory by NASA and other governments to push forth the false idea of CO2 caused global warming”. I have not attacked his theory much but I was asking where he got some of his assumptions (plant respiration is negligible in terms of exotherm vs the endotherm from photosynthesis and we just need to stop polluting the oceans with plastics and let plants do their job). I am about to go read your CO2 an insignificant trace gas posts. What are your thoughts on his disproofs? I read a small portion of the Gerlich rebuttal of Halpern’s comments on his paper and Mr Coats sounds a lot like Gerlich in his dismissal of well everyone but the people that agree with him. I don’t think I could say anything to dissuade him at this point as he just seems to go from engineering site to engineering site to start arguments. I just want to make sure I understand his flaws.
I can repost this under one of the CO2 discussions if you would prefer?
Noel: You aren’t likely to have any intelligent discussion with a guy like Coats that lists more than a dozen faulty and simplistic arguments about why rising CO2 can’t cause warming. If you are bothered by any one of his arguments (or you can get him to pick one argument at a time that he finds most convincing), then someone might be willing to help you address it. However, the real problem is confirmation bias – many people have a difficult time assimilating and recalling information that conflicts with their deeply-held beliefs – which often originate from politics, not science. With more than a dozen argument, Coats won’t be able to recall the any flaws you might point out in Rational #1 by the time you get to Rational #4.
Gerlich also discusses a variety of rationals and the same advice applies there.
Yes I agree, I just wanted to learn more for myself so I think I’ll just continue to read the backlogs here. Any other sites you recommend? Coats argument for the cause of global warming is basically the decrease in photosynthesis from mass plant death, not CO2 concentration changes. I tried to discuss his assumption to neglect plant respiration and he said “we have oxygen in the atmosphere”. I pretty much stopped talking to him there and then got lost down the rabbit hole of science!
Mass plant death??? That’s definitely going to be the funniest thing I’ve heard today and possibly in quite some time. All indications are that total active (alive) biomass has increased a lot over the last few decades. You’re not going to convince someone who believes that to change his mind about anything. I’m reminded of the paper I saw some time ago which claimed that when the CO2 level in the atmosphere went above 400ppmv, we were all going to die. Apparently the author was unaware that the CO2 level in nuclear submarines on long underwater missions reaches about 2%.
Yes DeWitt he is quite convinced that if we stop wasting money on the whole CO2 “conspiracy” and just regulate dumping, increase plastics recycling, and stop deforestation and death of marine plants we’ll be ok because the increased photosynthesis of the plants not being killed off by pollution will cool the earth eventually and reverse the warming….
Every blog has an agenda that motivates the host to do the work. Our host was motivated to explore the fundamental physical processes important to climate change. If that is what you want to learn, you are in the right place. When comments suggest that a message wasn’t getting through, the host addressed the issue. I personally find it hard to find this I remember reading (clever titles make this more challenging), so use the road map and consider reading series rather than chronologically.
From my perspective, climate change can be divided into two basis problems: 1) How GHGs slow radiative cooling to space – radiative forcing in W/m2. 2) How much warming is required to compensate for radiative forcing and restore balance at the top of the atmosphere – the climate feedback parameter measure in W/m2/K. The reciprocal of the climate feedback parameter is climate sensitivity which is reported in units of K/doubling rather than K/(W/m2). A summary of posts on radiative forcing can be found at the link below.
https://scienceofdoom.com/2014/06/26/the-greenhouse-effect-explained-in-simple-terms/
IMO, one of the biggest problems is that emission and absorption of radiation are taught as two separate subjects: 1) Absorption spectroscopy and Beers Law in the laboratory using a very intense light source to make emission negligible. 2) Emission of blackbody (which many don’t recognize is radiation where emission and absorption are in equilibrium. From absorption spectroscopy, we know that absorption by GHGs involves many lines or bands, but GHG’s certainly don’t emit a blackbody spectrum of radiation. The combined effects of absorption and emission by GHGs are calculated using radiative transfer calculations, but the equations and physics of those calculations isn’t commonly taught. After spending a long time putting a lot of pieces together that I was introduced to here, I tried to compress the fundamentals of radiative transfer calculations into the below Wikipedia article. (Since I haven’t gotten much feedback on the article, I suspect it doesn’t meet the needs of many readers.)
https://en.wikipedia.org/wiki/Schwarzschild%27s_equation_for_radiative_transfer
Thanks Frank!