Climate & Agriculture 5: Risk of declining (tropical) crop yields has been known for over 25 years

Not just from theoretical thinking, but as calculated outcomes of pioneering climate-crop prediction models – with studies from the early nineties already offering broad patterns of expected changes in agricultural productivity in a warming world. These patterns have of course been fine-tuned by tireless research ever since but already look very familiar to those who follow today’s climate impact research. And that’s something we think deserves our attention…

The influence of climate change on the growing season in a typical temperate, subtropical, tropical and desert climate. Taken from climate model study from 1993.
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Climate & Agriculture 4: Yes, heat stress also affects wheat – recent European summers show

Part 3 of this series about the impacts of climate change on global agriculture was centred around a climate model study that indicated major global crop belts could experience production declines as a result of increased heat stress. These authors found strong results for rice, maize, soy – but not for wheat.

That got us digging. Never trust good news, when it comes to climate change.

Wheat productivity declines under climate change
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Climate & Agriculture 3: Temperate and subtropical agriculture equally affected by heat stress

Our previous post focused on a study indicating climate change can lead to a net decline in African agricultural productivity – at least for five major food staples, with maize being the most important. The study also showed that it is not precipitation changes, but heat stress that is the main concern.

That is not a uniquely African problem, nor a problem that is constrained to the tropics. Paradoxical as it may seem, increasing heat stress is set to create comparable declines in agricultural productivity in colder (subtropical and temperate) climate regions – affecting other global food staples, like wheat, rice and soy…

Heat stress damage from climate change for 4 global food staples
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Climate & Agriculture 2: African net agricultural productivity to decline for 5 major food staples

The impact of 21st century climate change on African agriculture deserves special attention, considering rapid population growth and the fact that the continent is currently already a net importer of agricultural products, while several sub-Saharan countries still depend for a third to over half of their GDP on agricultural output.

Climate change poses an additional stress for these highly dependent nations: for 5 of the 7 most important sub-Saharan food staples (maize, sorghum, millet, groundnut, and cassava) already by the year 2050 significant productivity reductions are expected – decreasing average production between ±22 and ±8 percent, per respective crop:

Climate change to decrease net agricultural productivity major food staples in Africa
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Climate & Agriculture 1: African food imports increase, while agricultural dependence stays high

Yes, we have many simultaneous climate series running here at Bits of Science. For instance one about the global temperature trend, another about sea level rise – and of course our series about climate change as a driver to the Anthropocene Mass Extinction (part 47 published last week).

Today we have decided to start another one – about yet another important field where our climate interacts with another crucial system: agriculture. Our main interest will be net productivity, while keeping in mind we have to feed a growing human population on a decreasing amount of land, considering the simultaneous extinction crisis.

African food imports are dramatically increasing
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Despite warming trend, Europe can expect several frosty winters – as solar activity drops to minimum

Northwest Europe can expect a couple of winters with relatively frosty conditions, as one key driver of the North Atlantic Oscillation (NAO) is set to favour blockades of westerlies, allowing periods dominated by a supply of cold and relatively dry polar or continental air to flow in from the East or the North.

Current sunspot observations show solar cycle 24 comes to a close, entering a new - and possibly prolonged solar minimum. Image: NOAA.
Current sunspot observations show (the relatively weak) solar cycle 24 has come to a close, entering a new – and possibly prolonged solar minimum. In this article we discuss ramifications for pending European winters.

Based on the developing closure of the current solar cycle (number 24), a relatively long minimum and taking into account a documented time lag these effects may be observed for a relatively large cluster of winters, starting in 2019 and possibly lasting as long as 2026. Do to increased likelihood of a negative phase in the NAO for Northwest Europe these winters may be relatively cool – but not extremely cold:

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Climate Change & Anthropocene Extinction 47: Can species adapt by changing their fitness curves?

As we discussed in our previous article, ecologists use the term ‘fitness curve’ – or the synonymous ‘performance curve’ – to describe a climatological bandwidth within which a species can survive, including an optimum value and a critical minimum and maximum:

Fitness curve offers clue to species adaptation to climate change
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Climate Change & Anthropocene Extinction 46: Tropical insects vulnerable due to narrow fitness curve

You would think tropical species like warm weather – and what’s the difference between warm and 2 or 3 degrees warmer. Well, they can be picky. A short appendix to our previous article – a bit of supporting theory as to why tropical insects may be extra vulnerable to the effects of climate change.

Comparing fitness curves and climate change vulnerability for tropical and temperate insects.
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Climate Change & Anthropocene Extinction 45: Massive die-off tropical insects direct result of warming

Climate news does not get worse: new field data show total insect (and other arthropod) biomass in Central American rainforest has declined 10 to 60 times since the 1970s. Meanwhile also insectivores, like lizards, frogs and birds, are rapidly declining in the Luquillo rainforest of Puerto Rico. The driving force: climate warming.

Rapid insect decline in Puerto Ricon rainforest as a result of climate change
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Isostatic rebound Amundsen Bay: a negative feedback that acts on West Antarctic grounding line retreat

In our series ‘Understanding Sea Level Rise’ we’ve paid ample attention to positive melting feedbacks, mechanisms that accelerate ice melt and ice sheet dynamics as global temperatures keep rising. Now of course there are also negative feedbacks, like local relative sea level lowering around ice sheets (due to decreasing gravitational pull and isostatic rebound as the ice mass shrinks), a factor that can influence the position of the grounding line of West Antarctic glaciers, the line that separates where these glaciers move across bedrock and where they start floating, forming ice shelves. In general these grounding lines are retreating as a consequence of a warming water wedge and thinning of the ice shelves and the actual ice sheet, however the local relative sea level lowering as a result of this ice loss has the opposite effect, promoting an advance of these grounding lines – therefore acting as a stabilising factor for West Antarctic glaciers, like the Twaites Glacier and Pine Island Glacier, glaciers that are potentially important contributors to acceleration of 21st century sea level rise.

Now we presume you want to know which feedbacks are (likely to be) dominant in this area, the positive or the negative feedbacks. Well, apart from reading the title of this article you can also click it, to learn more…

Grounding lines under West Antarctic Ice Sheet
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