We’ve all heard the stories about climate
change. The Paris Climate Change conference remained in the news over the last
two years, first as it aimed to limit global temperature increases to
2 °C, and again when President Trump withdrew from the accords. Yet even
by the Paris Conference standards, this temperature increase could result in
sea level rises of between 3 and 6 meters by 2100. As it turns out, those
climate models may have failed to account for some things…
Two weeks ago, a team of researchers from
17 countries published a paper in Nature Geoscience, entitled “Palaeoclimate constraints on the impact of
2 °C anthropogenic warming and beyond.” Essentially, what these researchers
did was study the changes in the paleontological record of the earth (fossils)
before and during the last three times the planet experienced climate change
due to temperature increases in the same range.
The researchers looked at the Holocene
Thermal Maximum (HTM) which occurred between 5 000 and 9 000 years
ago, the Last Interglacial period (LIG), occurring about 129 000 and
116 000 years ago, and the mid-Pliocene warm period (MPWP), which occurred
about 3.3 to 3 million years ago. The HTM and LIG events occurred due to
changes in the earth’s orbit, but the MPWP had occurred due to atmospheric
carbon dioxide concentrations of about 350 to 450 parts per million – or about
the same as we have today. Of course, it took quite a bit longer for nature to
reach those levels. By combining data from ice cores, fossil records, sediment
layers, radiometric dating and other paleoclimate methods, they were able to
paint a picture of what a warmer earth will look like once global warming has
stabilized.
In terms of polar ice sheets, they found a
significant retreat of the Greenland and Antarctic ice sheets during those
times, giving a global sea level 6 to 9 meters higher than currently. In terms
of sea ice, it appears that a reduction of more than 50% was seen, which would
indicate much warmer waters. These warmer temperatures caused changes to the
marine plankton ecosystem, with a rearrangement of the surface-level habitat.
Plankton started to migrate poleward, and experienced blooms in surface waters.
On land there were large changes as well.
Most regions experienced a poleward shift of their biomes, as moisture regimes
changed. The Sahara desert greened, and eventually vanished. The Great Plains
of North America grew arid. The tundra and forest boundaries in the Americas
and Asia shifted northward by about 200 kilometres. Even here in Africa, the
Nama Karoo and fine-leaved savannah expanded. Across the globe, tropical
climates and savannahs expanded as deserts shrunk.
Just these changes could have profound
effects for our current nations – farmland becoming unviable as other countries
gain them, seafront property in danger – but the fossil record shows the real
danger. While humans may be causing an increase in atmospheric carbon dioxide,
nature will amplify it. A large amount of carbon is currently preserved in peat
– partly decomposed plant matter. Large peatlands are maintain in forests and
tropical climates as old plants died and form layers upon layers of them. This
makes it the largest carbon sink on the planet.
Peat, however, mostly forms where it’s wet –
it’s a wetland phenomenon, after all – and with the increase in temperatures…
Well, in the north, peat is usually protected by permafrost in the coldest
climates. With widespread permafrost thaw, the peat will release more carbon
than it absorbs, accelerating global warming. In tropical regions, climates
will move, and savannahs will expand. Fine-leaved savannah that’s quite
flammable, especially in warmer weather, and will release massive amounts of
carbon into the atmosphere in continent-wide wildfires if it burns over former
peatlands. These fires will devastate the edges of tropical forests, slowly
turning the entire area into fire-maintained savannah and grassland ecosystems
in the wake of natural deforestation. A rapid run-away change towards treeless
landscapes will result.
"Even
with just 2°C of warming -- and potentially just 1.5°C -- significant impacts
on the Earth system are profound," said co-author Prof Alan Mix of Oregon
State University. "We can expect that sea-level rise could become unstoppable
for millennia, impacting much of the world's population, infrastructure and
economic activity."
"Climate models appear to be
trustworthy for small changes, such as for low emission scenarios over short
periods, say over the next few decades out to 2100. But as the change gets
larger or more persistent, either because of higher emissions, for example a
business-as-usual-scenario, or because we are interested in the long term
response of a low emission scenario, it appears they underestimate climate change,"
said co-author Prof Katrin Meissner, Director of the University of New South
Wales Climate Change Research Centre.
We here in Namibia have already experienced
stranger and stranger weather patterns over the last decade. We’ve often heard
of the so-called butterfly effect in weather forecasting – how a butterfly
flapping its wings in Tokyo can cause a rainstorm in Johannesburg – and how it
shows that long-term weather forecasting is a pipe dream. In more manageable
terms, it explains how small changes in initials conditions can result in
widely different outcomes in future. This paper shows another side to that –
small changes now can have drastic effects on our planet in future. Yet it also
gives us a bit of hope. Maybe, by making small changes now to our world, we can
flap our wings, and change the outcome for our planet, and ourselves.
