Mediterranean Desert

A new paper in Science bears the innocuous title Climate change: The 2015 Paris Agreement thresholds and Mediterranean basin ecosystems [Guiot & Cramer, Science, 354(6311), 465-468, DOI:10.1126/science.aah5015], but comes to the disturbing conclusion that if the world exceeds the 1.5°C threshold, much of the Mediterranean region will not be able to sustain the ecosystem in which it has thrived for 10,000 years. In particular, it may suffer from reduced rainfall and see now-fertile land turn into extensive desert.

Reduce rainfall isn’t the only factor influencing drought and desertification. So too is plain old heat; rising temperature increases evaporation and dries out the land, making droughts which come to pass more severe. When the two factors combine, less water coming in and more evaporating away, desert can replace what was once green.

Not only has the land area around the Mediterranean been warming along with the rest of the globe, recently it has been warming faster than average. I retrieved temperature data for the Mediterranean land region from the Berkeley Earth Surface Temperature project, and found this:


When compared to the world as a whole, we find that this region is warming faster even than the globe’s land areas:


The warming rate since the mid-1970s is about 0.037 deg.C/yr, compared to the average land-area warming of 0.029 deg.C/yr.


Even without a decline in rainfall, the region will suffer mightily from temperature increase. The expectation of too little water makes the situation genuinely frightening, and that’s the prospect the abstract makes clear:

The United Nations Framework Convention on Climate Change Paris Agreement of December 2015 aims to maintain the global average warming well below 2°C above the preindustrial level. In the Mediterranean basin, recent pollen-based reconstructions of climate and ecosystem variability over the past 10,000 years provide insights regarding the implications of warming thresholds for biodiversity and land-use potential. We compare scenarios of climate-driven future change in land ecosystems with reconstructed ecosystem dynamics during the past 10,000 years. Only a 1.5°C warming scenario permits ecosystems to remain within the Holocene variability. At or above 2°C of warming, climatic change will generate Mediterranean land ecosystem changes that are unmatched in the Holocene, a period characterized by recurring precipitation deficits rather than temperature anomalies.

There’s something about the phrase “unmatched in the Holocene” that I find quite worrisome.

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21 responses to “Mediterranean Desert

  1. As if the Middle East weren’t volatile enough…

    • perfect storm in much of the middle east: terrible climate impact, loss of crops and growth of food and economic insecurity with the additional misfortune of oil reserves that encourage global powers to manipulate the region for benefit of folks who live elsewhere. It’s bad, it gets worse. We need a miracle direct air capture tech breakthrough now. Keep that one on top of list in your prayers.

      • a miracle direct air capture tech

        No matter how close to a miracle it is, it will never be free so who is going to pay for it?

      • …who is going to pay for [direct air capture]?

        Ideally, who ever wants to emit the carbon. For instance, if the carbon from one gallon of jet fuel costs $10 to capture then that price would be added on to the ticket, and then someone else would get the money for capturing the carbon. So far I have almost no clear idea of how much that is – I’ve seen estimates of $10/ton through $3000/ton. This is a key area that needs more research.

      • who ever wants to emit the carbon

        So there are lots and lots of carbon-emitting people around thinking “I hope someone comes up with a miracle direct air capture tech breakthrough because then I will pay to have my carbon emissions captured”.

        I won’t be holding my breath waiting for many people to do that.

      • who ever wants to emit the carbon

        So there are lots and lots of carbon-emitting people around thinking “I hope someone comes up with a miracle direct air capture tech breakthrough because then I will pay to have my carbon emissions captured”.

        I won’t be holding my breath waiting for many people to do that.

  2. David B. Benson

    Yes, the Spanish, Italian and Greek extensions to the Sahara. Not to mention the end of the Maghreb.

  3. Sadly we are expecting the same scenario in the mega-diverse biodiversity hotspot of south-west Western Australia, which also has a Mediterranean climate. In that case the climatic zone that supports forests, woodlands and heathlands with per-hectare species diversity rivalling tropical rainforests will be pushed of the continent into the southern ocean.

  4. “…if the world exceeds the 1.5°C threshold…”

    The bit I can’t understand is why people keep talking as if this is still in question: if the land-only temperatures have already passed 1.5 °C then surely it’s just a matter of time for the water to warm up and the ocean and global temperatures to follow along. The high heat capacity of the oceans and decade-to-decade variation might mean it takes a while to get there but we have a clear indication, I think, that if we stay at about 400 ppmv, let alone increase beyond it, then 1.5 °C is all but inevitable.

    • Some folks think we will find sufficiently feasible ways to draw down CO2, and deploy them. I suppose it’s at least possible, and I hope they are correct. But task #1 is to mitigate our emissions, and for that, the sine qua non is to organize, organize, organize (politically.) One option:

  5. What would warming rate of the whole earth surface be?
    The rates you extracted mean 3,7 K/100y and 2,9 K/100y, respectively, which is quite outrageous.

    [Response: Those are rates for land area only, for the Mediterranean, and for the globe. The entire globe including both land and ocean areas is about 1.7 K/100y.]

  6. The biggest, simplest and healthiest life style change that you can make to cut emissions is to give up eating animal products. But I bet over 90% of you won’t do it unless you’re forced to.

    • Sorry, it is not true. Emissions arise from many sources, so you need to act on different fronts at the same time. Plus, not all meat has the same impact. Poultry, for example, is quite acceptable in terms of GWG emissions.

      Go ahead with your meat-less lifestyle, I’ll tgank you, but don’t think this can compensate for a V8 Mustang commuter.

    • I’ll bet most Americans won’t give up either animal products or fossil fuels until their prices internalize the cost of AGW.

  7. “Emission intensities (i.e. emissions per unit of product) vary from commodity to commodity. They are highest for beef (almost 300 kg CO2-eq per kilogram of protein produced), followed by meat and milk from small ruminants (165 and 112kg respectively). Cow milk, chicken products and pork have lover global average emission intensities (below 100 CO2-eq/kg.) (At the sub-global level, within each commodity type there is very high variability in emission intensitys, as a result of the different practices and inputs to production used around the world.” Silly me I thought I was addressing the whole world via the internet so the average person not just the USA. However, the average American consumes well over 100g of protein per day, about 60% red meat and 40% poultry. So that’s at least 15kg CO2eq per day, equivalent to about 6 litres of gasoline. Does the average family of 4 use +/- 20 litres per day? (I’m guessing children consume a little less protein per day.) And then of course there’s dairy products as well…

    • “Does the average family of 4 use +/- 20 litres per day?”

      We used to, with 2 adults commuting in 2 different directions for a round trip total of ca. 160 miles. We probably got 20 mpg or so back then, so 8 gallons or 30-odd litres. Not that unusual for suburbanites in America.

  8. According to the FAO, the average American consumes 110 grams of protein per day of which 70 grams is animal proteins. That means 40 grams comes from vegetables: that’s 80% of the RDI. See page 64 of the FAO Report

  9. This is a bit off topic, but on the subject of deserts, and since Australia came up in the comments, it is a little known factoid that the UK, in the process of giving up/selling off anything and everything of value and polluting the commons for short-term gain, has leased out mineral rights to vast quantities of Yorkshire to climate billionairess Gina Rinehart. She’s smarter than Trump, but cut from the same selfish cloth. Anybody who wants to know more about one of the most awful people on the planet can read this:

    Can’t win for losing. We don’t have enough native exploiters, we have to import them. Well, I’m from the US, but my sympathies are with the beleaguered dumbasses who are stuck with Brexit because people don’t think. Prices are now going up, and jobs disappearing, in the UK. That’s what happens when you ignore reality and vote your most negative emotions.

    • So the “most negative emotion” must be a desire for national sovereignty rather than rule by a financial cartel. As I have said: science here great, but the politics, Oy!

  10. This is all so frustrating.

    Time and time again I see science deniers, whether outright denialists or the probably more pernicious lukewarmers, exhibit complete ignorance or misunderstanding of the sensitivity of species, communities, and ecosystems to small changes in temperature. And this is just the most basic aspect of thermal ecophysiology… Mean temperatures may themselves demonstrate little change but perturbations in variability – especially of extremes – or changes in the timing of temperature changes can have profound proximal and distal impacts.

    And then there are the impacts of precipitation and soil moisture that follow on from changes in temperature, and the knock-on to the movements of nutrients in trophic webs…

    What many lay people (and especially deniers) do not understand is that these impacts are already inexorably occurring, and in many cases impossible now to stop. Just because these folk cannot yet perceive them does not mean that they are not occurring. Humanity is clocking up a huge extinction debt, and putting in train profound changes to the ecosystem functions on which we rely, and the only thing that will help is immediate and serious action. Lukewarmism and denialism might make their proponents feel better, but are tools for the final destruction of our civilisation as we know it. And until we as a society can all understand the exquisite sensitivity of ecosystems to abiotic parameters on centennial to multi-millennial scales of time, and act on such, we are moving ever more surely to that destruction.