An addendum to the Statement on Climate Change: Evidence from the Geological Record
It's worse than we thought!
Since our original 2010 statement, new climate data
from the geological record have arisen which strengthen
the statement’s original conclusion that CO2 is a major
modifier of the climate system, and that human activities
are responsible for recent warming.
Palaeoclimate records are now being used widely to test
the validity of computer climate models used to predict
climate change. Palaeoclimate models can simulate the
large-scale gradients of past change, but tend not to
accurately reproduce fine-scale spatial patterns. They
also have a tendency to underestimate the magnitude of
past changes. Nevertheless they are proving to be
increasingly useful tools to aid thinking about the nature
and extent of past change, by providing a global picture
where palaeoclimate data are geographically limited.
Geologists have recently contributed to improved
estimates of climate sensitivity (defined as the increase
in global mean temperature resulting from a doubling in
atmospheric CO2 levels). Studies of the Last Glacial
Maximum (about 20,000 years ago) suggest that the
climate sensitivity, based on rapidly acting factors like
snow melt, ice melt and the behaviour of clouds and
water vapour, lies in the range 1.5°C to 6.4°C. Recent
research has given rise to the concept of ‘Earth System
sensitivity’, which also takes account of slow acting
factors like the decay of large ice sheets and the
operation of the full carbon cycle, to estimate the full
sensitivity of the Earth System to a doubling of CO2. It is
estimated that this could be double the climate
sensitivity
