IPCC AR5 – Summary for Policymakers 2012
Our AR4 report included the following statement:
The understanding of anthropogenic warming and cooling influences on climate has improved since the TAR, leading to very high confidence that the global average net effect of human activities since 1750 has been one of warming, with a radiative forcing of +1.6 [+0.6 to +2.4] W m–2 "
We further estimated an increase in temperature of about 3 degrees C. for a doubling of CO2.
We now realize that our knowledge of the factors controlling earth’s climate is much more limited than we previously thought and we are at this time unable to calculate the possible future effect of anthropogenic CO2 with any degree of certainty useful for policymakers. We apologise to those policymakers who embarked upon economically destructive carbon emission control schemes based upon our previous statements and similarly apologise to those members of the western intelligencia who spent sleepless nights worrying about the fate of the planet and their days trying to reduce their carbon footprint.
We can however make some possibly useful comments with suggestions for policymakers .
It is now clear that the patterns of the earths ocean current systems provide the best guide to the current state of the climate and the best clues as to developments over the next 20 – 30 years. Beyond that time span predictions are of little practical value.
Of particular note is the negative phase of the PDO which began about ten years ago and may well last for another 20 years. This suggests that La Ninas will be more frequent than El Ninos during this time span. A general earth cooling is thus more likely as was the case from 1940 to 1970 when similar conditions prevailed. Concurrent changes in the Arctic Oscillation suggest a pattern of meridional atmospheric flow will be more common than the more latitudinal flows of warmer periods.
In addition the sun has entered a quiet phase with a dramatic drop in solar magnetic field strength since 2004. This reinforces the probability of a cooling phase on earth.
Policymakers may wish to note the following possible effects on earths climate for the next 20 – 30 years. A cooler world with lower SSTs usually means a dryer world. Thus droughts will be more likely in for example California, and east Africa with possible monsoon failures in India. Northern Hemisphere growing seasons will be shorter with occasional early and late frosts and repeats of the harsh Central Asia (Mongolia) winters of 2009 – 10 . Cold European winters and cool cloudy summers will be more frequent .
There will be a steeper temperature gradient from the tropics to the poles so that tornadoes will be more violent and more frequent in the USA, At the same time the jet stream will swing more sharply North – South thus local weather world wide will be generally more variable with occasional more northerly heat waves and more southerly unusually cold snaps. In the USA hurricanes may strike the east coast with greater frequency.
Arctic and Antarctic sea ice may react differentially to an average global cooling. We might expect sea ice to increase in the Antarctic but the Arctic Oscillation while bringing cooler temperatures further south may also bring warmer air into the Arctic with possible loss of sea ice in that area.
The most general advice is that world food production may be subject to occasional serious severe restriction because of cold and drought. The use of food crops for biofuels should be abandoned and stockpiles built up for possible lean times ahead. Northern cities and transportation systems should prepare for more frequent heavy snow and ice storms.
There is no threat from the burning of fossil fuels for the forseeable future, indeed an increase in CO2 would positively help in feeding the burgeoning population.
For the next 20 years climate science should be devoted to improving and enlarging the entire climate data base in particular with regard to solar data of all kinds. No climate model runs should be made until 2025 by which time the inputs will be more relevant to the real world.