Note: This program first aired January 31, 2015.
It may be no surprise to you that anthropogenic climate
change is paying dividends to the world already. No longer is this something we
can think of as impacting the future. The future, as they say, is now. World
wide glaciers, both continental and alpine are in rapid retreat, phenological
changes that include earlier dates of ice out on lakes and rivers and earlier timing
of spring tree, flower and phytoplankton blooms are being documented everywhere,
tropical diseases are spreading, along with their host insects to higher
latitudes whose climates can now support them, the intensity and frequency of
extreme heat waves are increasing, Arctic sea ice is getting smaller and
thinner each summer, and last year was the warmest year on record.
When we think about the consequences of climate change, there
are two models that are used to conceptualize what might happen (as well as for
comparison with what IS happening). The first model is linear. In this world
view, incremental increases in green house gasses yield incremental changes in
climate, it’s a y equals mx plus b vision of how the climate system works. The
carbon dioxide level and average global temperature have a direct relationship.
As carbon dioxide levels increase, average global temperature increases at some
set proportion described by the slope of the line, and that relationship
remains a constant straight line regardless of how high carbon dioxide levels
get. It is a reassuring, predictable relationship, in that the math is simple.
If we know the X value, a carbon dioxide level, we can get a Y value, the
resulting temperature. Everyone can interpret a straight line graph. It’s worth
noting that this is the model that the Intergovernmental Panel on Climate
Change, the world’s preeminent climate change research and policy body, uses to
makes its predictions, predictions that direct the course of global policy
actions.
The problem is that Earth’s climate system is not actually
linear. The relationship between carbon dioxide and temperature may appear to
have simple causal attributes, but it is just the tip of the iceberg. Climate
is defined as the long term average of weather, and weather is acknowledged to
be a chaotic system, chaos in this sense as a technical term, meaning
distinctly non linear. As we increase atmospheric carbon dioxide and thus
increase average temperatures as expected, all kinds of other related processes
can get triggered, and lead to rapid and unexpected effects. Take for example,
last year’s intensely cold winter in North America, not the kind of thing you
would expect if you used the simplistic model of increasing carbon dioxide
leading to warmer temperatures. In fact the increasing temperatures have
disrupted typical atmospheric pressure arrangements and thus wind patterns,
which led to changes in the jet stream. Instead of running primarily west to
east last winter, the jet stream (which is simply the boundary between polar
and mid latitude air masses) was able to take large north and south running
loops, bringing very dry cold polar air to lower latitudes than we are used to.
Chaos.
The ultimate expression of this non linear climate system,
and the one that keeps climate scientist up at night is the model of abrupt
climate change. It’s what many leading climate scientists see on the very near
horizon. Essentially X leads to Y, which then leads to A, B, C or any other
letter in the alphabet, or perhaps, all of them. A warming average global
temperature pushes certain aspects of the climate system past their tipping
points, which result in a rapid and more irreversible change in the functioning
climate system. Those anticipating abrupt climate change are looking hard at
what is happening in the Arctic. Polar amplification has long been recognized,
in that the Arctic has seen warming temperatures several degrees higher than
the global averages, due largely to feedback loops related to the loss of sea
ice and therefore albedo. As less sunlight is reflected (because there is less
highly reflective ice around), more light is absorbed, which then warms the
Arctic and melts yet more ice. There are suggestions that the Arctic may be
more intimately influential in global climate than was previously suspected,
and if the Arctic continues its death march towards a tipping point, it may
take the whole world with it, quickly. There is precendent for the mechanisms
of abrupt climate change in the paleoclimate record, abrupt climate change is
in fact what has led the Earth into glacial periods, as well as to rapidly
emerge from those same ice ages over a matter of decades.
Over the past many many weeks and months we’ve spent most of
our climate change energy focusing on the carbon, because quite simply, this
whole thing starts with the carbon, it’s the crux of what is driving the
warming of the climate. The parallel story is that while carbon is simple,
climate is wildly complex and the system is massively difficult to describe
quantitatively in terms of predicting behavior. That is why climate scientists
are a strange mix of computer geniuses who build super computing climate
models, and field researchers who drill cores in glaciers and ocean sediments
trying to reconstruct past climate patterns. We look at the past to predict the
future, and the past tells us that it is likely an abrupt shift, rather than a
gradual stepwise transition, that we should be looking forward to.
References:
Current effects of climate change from NASA, including
several really good graphical representations of various effects: http://climate.nasa.gov/effects/
IPCC home page, read the projections for your self: http://www.ipcc.ch/index.htm
Maine Climate Change Institute on Abrupt Climate Change http://a2c2igert.umaine.edu/sample-page/what-is-abrupt-climate-change/
Thinking about adaptations: http://climatechange.umaine.edu/maine_clas_conference/
Tipping points: http://au.ibtimes.com/climate-change-arctic-could-trigger-domino-effect-around-world-1292935#.UqWaV_R9aSo
