It may already be too late to head off major famines in the mid-part of this century. That's one of the clear implications of the latest PricewaterhouseCoopers review of the world's carbon economy, Too Late for Two Degrees?
Two degrees of global warming may not sound much to most people, but combined with extreme weather events it is the point at which the world's food supply, and grain production in particular, begins to face serious jeopardy. And if grain runs short, the first thing to go is meat. So this isn't just an issue that will hit the poor and the already hungry: it will affect everyone who eats.
The report by PwC, one of the world's largest accounting firms, is blunt: ''Now one thing is clear: businesses, governments and communities across the world need to plan for a warming world - not just 2ºC, but 4ºC and, at our current rates, 6ºC.''
''This isn't about shock tactics, it's simple maths,'' PwC partner Leo Johnson told Canadian science writer Steve Leahy. The ''simple maths'' says the world has been cutting its carbon emissions at only one-sixth of the rate needed to avoid four to six degrees of global warming. In perspective: the US would have to eliminate all its existing coal-fired power stations in eight years to meet its share of the two-degree target - and much the same applies to Australia.
Its sober assessment has been echoed by a second major report, by the World Bank, which warned that places such as India could lose up to half their grain crops under 2 degrees of warming, and Africa a third of its arable area. It links 13 of the most devastating climatic events of this decade to man-made global warming.
The reports come just before the United Nations Climate Change conference opens in Doha on Monday, already shaping as another of those dispiriting affairs where pious sentiments, platitudes and good intentions substitute for concrete, decisive action by what is already rated as the least-effective worldwide political leadership in a century.
However, the real significance of these reports is that we are now looking down the barrel at climate-induced economic shocks that will make the global financial crisis look like a modest hiccup.
What some of those shocks might look like will be discussed by scientists attending the Second Australian Earth System Outlook Conference hosted by the Australian Academy of Science in Canberra, also on Monday. They will explore some of the ''tipping points'' where systems break down and shift to a new, more perilous, state. The focus will be on the continuing disconnect between climate science and society over carbon, impacts on the poles, the oceans, the Great Barrier Reef, and food security.
Food security is vital because that's the main way most people will personally experience climate change - as huge, unexpected rises in the cost of foods they had previously taken for granted, due to drought, flood, tempest or searing temperatures. So far, it appears the world has lost about 4 per cent to 6 per cent of its major grain harvests due to global warming.
What is not generally understood, however, is that global (and Australian) food security also depends on a series of scarce resources that are becoming increasingly unaffordable to farmers: land, water, oil, fertiliser, fish, finance and technology, to name a few. Climate change is now amplifying these emerging scarcities in unpredictable ways.
For example, it is probable that key regions of the world will run out of water in the next 10-20 years - the north China foodbowl, the Indo-Gangetic plain, the US midwest and the Middle East. These could trigger mass migration by tens of millions of people as well as the outbreak of local conflicts, as numerous military studies now attest. Climate change, with its sudden, unanticipated impacts, will exacerbate water scarcity and flood destruction of food systems. The bit the world's policymakers don't seem to get is that these impacts are synergetic and cumulative, reinforcing and compounding one another. They cannot be solved by one-off ''fixes'' such as water markets, fuel subsidies or GM crops.
To put this in personal perspective, you consume each day 4.1 litres of diesel fuel, 29 kilograms of soil and 2.2 tonnes of water in the form of food. If any of these things run short, here or globally, your supermarket bill will tell you all about it. Yet governments here have quietly been dismantling Australian landcare, irrigation and agricultural science as if they did not matter.
Such complacency mirrors the attitudes of governments globally on climate change - either in preparing for the worst or in attempting to prevent it. Humanity, paralysed by an incoherent and acrimonious media debate where ideology predominates over evidence, knowledge and wisdom, is sliding helplessly towards what PricewaterhouseCoopers policy expert Jonathan Grant terms ''the carbon cliff''.
On the brighter side, however, PwC clearly identifies green technology as the most likely driver of the next big global investment wave - as China and Germany are already demonstrating by their huge swing to solar. Australia, the nation with more free photons per square metre than anyone else on Earth, still lurks among the also-rans and ne'er-do-wells: what is it with us, that cloudier countries see more opportunities in sunshine?
However, it is food, not energy, that will deliver the ultimate wake-up call - to Australians, Chinese, Americans, Indians, everyone alike. That is the message that needs to come out of Doha. Climate change is getting personal. It's already on your dinner table and in your wallet.
Julian Cribb is a science writer and author of The Coming Famine: The Global Food Crisis and What We Can Do to Avoid It (UCP 2010).