It may not be a consensus, but the collective view of the world’s climate scientists is that humans are responsible for the bulk of the change observed over the last century. And the scientists concerned have now firmed up their previous statements on the matter.
One of the professional organisations to which I belong is the American Geophysical Union (AGU). Despite its name, the AGU is a truly international body, and you would be hard-pressed to find an active geoscientist who isn’t a member. No longer working myself as an atmospheric physicist, I keep up my subscription as the AGU is a mine of useful information and networking possibilities.
Just over a week ago the AGU released a statement updating its 2003 position on climate change. You can read the document here, and I recommend that you do so. Free of hyperbole and political bias, the statement is well-written, and perfectly comprehensible by sentient humans of average intelligence and above.
Here is an extract:
“In the next 50 years, even the lower limit of impending climate change–an additional global mean warming of 1°C above the last decade—is far beyond the range of climate variability experienced during the past thousand years and poses global problems in planning for and adapting to it. Warming greater than 2°C above 19th century levels is projected to be disruptive, reducing global agricultural productivity, causing widespread loss of biodiversity, and—if sustained over centuries—melting much of the Greenland ice sheet with ensuing rise in sea level of several meters.”
The statement goes on to say that if this disruptive warming is to be avoided, then we will have to reduce our net carbon dioxide emissions by more than 50% this century. Note the use of the words “more than”. Fifty percent really is a best case scenario, and the chances are that the figure will have to be revised upwards as we learn more about ice dynamics and a number of other factors.
The statement goes on:
“Given the uncertainty in climate projections, there can be surprises that may cause more dramatic disruptions than anticipated from the most probable model projections.”
So now you know (if you didn’t already).