UNDP’s Rapport mondial sur le développement humain 2006 (PDF) – which focuses on the global water crisis, is just one example of a model-based climate-impact study that shows net decreasing North-African food production as a result of continued global climate change. This study shows decreased cereal productivity on both sides of the Sahara desert. There is high uncertainty about the East Sahel though [B]. Also the speed of change might be on the conservative side [A] – see below for elaboration on both matters.

Climate warming-induced Hadley cell expansion behind decreasing agricultural productivity in the Middle East and both on the European and North-African side of the Mediterranean

That was to draw your attention. If you found that title a tad hard to understand: the Sahara is moving North almost says the same.

Under continued climate change the world’s net agricultural productivity is likely to decrease. This is caused not only by increasing drought and direct (summer) heat stress, but also by increasing weather extremes (heat waves, storms, floods) and climate-induced plagues.

The Mediterranean and Middle East are increasingly swallowed by a northward shifting (and net increasing) arid zone. This shift is caused by global climatic warming that leads to higher energy in the general circulation: The Intertropical Convergence Zone (ITCZ) – known more commonly as monsoon – increases in strength due to increased convection and convergence. More convection means tropical rainstorms grow higher. This in turn also leads to lateral growth of the Walker Cell – and therefore pole-ward migration (on both hemispheres) of the subtropical subsidence zone, where air under downward force is compressed at the Earth surface and semi-perminent high pressure systems lead to strucutural drought and desertification. This zone has formed the Kalahari, Sahara and Arabian deserts – deserts that are likely to all migrate in pole-ward direction, eating away at ecosystems and agricultural productivity in their paths.

A. You reap what you sow: climate-impact studies no given – you get what (scenario) you (chose to) emit. But let’s not be foolishly optimistic:

Disclaimer/reality check: many established (UN) climate impact studies still refer to the old IPCC special report on emission scenarios (SRES), dating back to the year 2000. That means most climate impact studies tend to have an ‘optimistic bias’. Here’s why: IPCC emission scenarios are caught up by reality.

The often-used A2 scenario family from IPCC SRES (‘A world of independently operating, self-reliant nations / continuously increasing population./ regionally oriented economic development‘) was in the year 2000 thought to lead to CO2 concentrations between 520-640 ppm by 2050.

We now know (thanks to the new IPCC assessment report of 2014 (AR5)) that even to get to such [unacceptably high!] concentrations, urgent global emission reductions are needed [see this graph] over the time frame of the new UN climate treaty, to be established at COP21, the Paris climate summit in December this year. This treaty is to guide nations on a chosen CO2 path towards to year 2030 (and of course beyond).

Two days ago we saw that current 2030 emission reduction commitments by countries [another important graph!] (submitted to the UNFCCC for COP21) are grossly insufficient to stay within scientific reach of the internationally agreed 2 degrees climate target.

Why this long introduction? To illustrate that the above map of North Africa serves to show a dramatic trend under continued (unabated) climate change – but that perhaps we shouldn’t focus too much on the numbers in it. If the world keeps burning fossil fuels at current rates, things will be worse, faster.

B. Hadley cell expansion also leads to generally wetter tropics, possibly including East Sahel

Climate change equals climate disruption – is never good. People can adapt to some extent, nature can’t.

Still it is important to note the world is not ‘drying up’ due to climate change. In general dry areas become drier, high-precipitation areas become wetter.

But there are even important exceptions to this rule, many climate studies show. Because of the orientation of land masses, mountain ranges and oceans – general climate warming will also lead to meanders in the above-mentioned ITCZ. Pollution-induced monsoon disturbances over Indiaarea well-known example. If the Indian monsoon gets stuck over the Indian subcontinent the South will experience increased floods – while the North might suffer increased droughts.

We’ve also talked about the opposite effect over South America – with damaging consequences. When the ITCZ is sucked northwards the Amazon will dry out (even faster) with a likely biome shift from tropical rainforest to savannah [and dramatic biodiversity loss and extra CO2 emissions as a result].

While the Amazon dries out parts of the eastern Sahara and eastern Sahel regions might actually see an increase in precipitation, due to northward meanders of the ITCZ over that region. The result is shown in the above map of annual precipitation changes.

UNDP updates that take into account possible wetting of the East Sahel draw a different map (as shown above) – where cereal production might benefit in that same region. West Africa and the north side of the Sahara desert continue to see projected agricultural decreases in these studies.

‘Climate refugees’ – two dramatic trends adding up?

When you have a fast-growing population (see this graph for Africa – see this article for Arab Spring countries) and decreasing food production, instability is the logical outcome. That includes not only conflict, but also mass migration of people.

According to IPCC AR5 (2014) Africa is currently warming at 0.2 degrees per decade, a warming that may increase to 0.5 degrees. Judging by UN Population Division projections this warming trend is accompanied by a population surpluss in the hundreds of millions of people – also per decade(!)

In the current debate about the European refugees crisis – some contributors say we are talking about a tip of an iceberg – and migration pressure is likely to increase dramatically due to climate change. Here we hope to show that we think these people are (likely) right, especially when you combine the climate trend with demographic trends. In the interest of global stability the world requires mitigation policy – most logically at UN level. For climate change we have a framework: the UNFCCC and even a date: COP21, December 2015, Paris. There is as yet no UN framework for demography – although at some point this might branch from the UNDP(?) – logically.

© Rolf Schuttenhelm | www.bitsofscience.org