Climate Change & Anthropocene Extinction 5: What are the IPCC predictions for biodiversity loss?

Climate change is a direct disturbing factor to ecosystem health. It also leads to geographical biome shifts and therefore forced species migrations. Invasive species and food chain disturbances can lead to plagues, creating further ecosystem damage. All these factors work synergistically with other current and future ecology stressing trends, like deforestation and ocean acidification, which makes it difficult to model and project biodiversity decline – yet all the more valuable to take notice of scientific attempts to come up with actual figures.

Ecological effects of climate change according to IPCC AR5 (2014)
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Climate Change & Anthropocene Extinction 4: Earth’s biodiversity may include >1,000,000,000,000 species(!)

Yes. That’s ONE TRILLION. ‘Possibly’ – as recent research using statistical scaling rules shows Earth’s total biodiversity, expressed in numbers of species, lies somewhere between 100 billion and (possibly more than) ten times as much. Welcome to the world of microbes.

Predicting total Earth biodiversity
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Climate Change & Holocene-Anthropocene Mass Extinction 3: Biodiversity is function of time and plate tectonics

Here’s just a quick supplement on yesterday’s article, showing Earth’s historical biodiversity graph correlates with different phases of plate tectonics.

Earth's biodiversity is function of time and plate tectonics
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Climate Change & Holocene-Anthropocene Mass Extinction 2: Biodiversity graph shows Garden of Eden is Now

Yesterday we tried to place the Holocene-Anthropocene Mass Extinction in the context of Earth’s past mass extinctions. Listing the Holocene Extinction as the ‘Sixth Mass Extinction’ proves problematic for various reasons. Today we offer additional context: although a mass extinction is defined as the loss of >75% of (larger) species – this definition does not take into account absolute numbers of biodiversity loss. To do so requires understanding of the net evolution of biodiversity.

The evolution of biodiversity on Earth
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Climate Change & Holocene-Anthropocene Mass Extinction 1: First of all, what are we talking about?

Yes, you’ve guessed it: a new series – and one we think is (even) more important than the previous climate series on Bits of Science, like our short (ongoing) understanding sea level rise series, and the more elaborate series about climate-temperature inertia (the ‘real’ global temperature trend).

This time we want to dig deep into the science of climate-ecology interaction – to try to develop a sense, based on facts, figures and research, of the Holocene Mass Extinction, and the role anthropogenic climate change plays as one of the main drivers of this escalating loss of global biodiversity.

Mass extinction events in Earth's marine fossil record
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Understanding Sea Level Rise, p4: ice sheet dynamics and (13) melting feedbacks – a background to 21st century SLR acceleration

In 2016 two influential new publications raised the possibility of a rapid acceleration of sea level rise in the 21st century – to ±2 metres (DeConto & Pollard) or more (2-5m, Hansen et al).

In this background article we take a look at both these studies – but also at 30+ other publications that we think are helpful to show the broader context: an increasing pile of evidence, coming from a world of science, indicating ice sheet dynamics are never linear and can be surprisingly rapid.

Looking at the key processes we show that the Hansen and DeConto studies add to a list of no less than 13 different (yet highly entangled, often synergistic) ice sheet melting feedbacks, feedbacks that can promote a rapid acceleration of global sea level rise:

Ice sheet dynamics and melting feedbacks. A meltwater river on Greenland, with climate researchers around
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Understanding Sea Level Rise, p3: it’s about timescales, speed of change & carbon budget – world aims for 29-55m sea level rise

In our previous article of the series we’ve looked at an overview of global sea level rise forecasts for the year 2100 – and seen that these forecasts have a very large spread, and also seem to increase with time of publication (from problematic (decimetres) to catastrophic (multiple metres)).

Today we show ‘the full story of anthropogenic sea level rise’ – a story that requires us to zoom out to much larger timescales, to learn to respect the immense thermal inertia of oceans and ice sheets while simultaneously coming to terms with the full magnitude of the sea level rise that our CO2 emissions in the 20th and 21st century are causing: that is 29 to 55 metres in total, depending on the amount of fossil fuels we choose to continue to dig up and burn.

Best sea level rise graph ever - Nature Climate Change
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What’s the (unnerving) similarity between 21st century forecasts for sea level rise and forecasts for world population growth?

They increase with time. And that suggests something is wrong with the science – something that needs to be uncovered.

21st century world population growth graph
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