Paris: Climate change refers to long-term weather patterns altered by heating of Earth’s surface. Natural warming is caused for example by volcanic activity and increases in solar output, and without it our planet would be too cold for human life.
But over the last few decades, evidence has grown ever stronger of an added, human factor: carbon gas emitted mainly by burning coal, oil and gas. It traps solar heat, causing the famous “greenhouse” effect.
WHAT ABOUT UNCERTAINTY?
In 1988, when a handful of US scientists drew attention to the risk, global warming was widely deemed a remote problem and one hedged with many unknowns.
Today, with major budgets devoted to research, many areas of uncertainty have shrunk or been eliminated, although some new ones have taken their place.
Experts overwhelmingly conclude that climate change is already happening, that carbon emissions are to blame, and that grave damage could result if these gases are not curbed.
The benchmark scientific opinion for this is the UN’s Intergovernmental Panel on Climate Change (IPCC). Its scientists write overviews of the evidence. The summaries of these massive documents are approved by governments, which are then supposed to use them as policymaking guides.
HOW BAD IS THE PROBLEM?
According to the IPCC’s latest Fifth Assessment report, atmospheric levels of three greenhouse gases are now higher than at any time in the last 800,000 years. Concentrations of carbon dioxide (CO2) have soared by 40 per cent since pre-industrial times, and are rising yearly.
It predicts temperatures will rise by between 0.3 and 4.8 Celsius (0.5-8.6 Fahrenheit) this century, depending on four scenarios for trends in carbon emissions. (Previous research says there was already warming of around 0.6 Celsius from the late 19th century to the start of the 21st century). Sea levels this century would likely rise between 26 and 82 centimetres, according to the scenario.
The outcome, again depending on the level of warming, will likely worsen floods and drought, species extinctions, loss of coastal land in small island states and health perils posed by heatwaves and water- and mosquito-borne diseases.
Hunger, homelessness and conflict over resources will be likelier, as well as extreme weather events.
Even temperatures of 1-2 Celsius above pre-industrial levels present risks that are “considerable,” according to the report. Beyond 4 Celsius, the impacts would be “severe and widespread”.
WHAT IS BEING DONE?
The planet-wide vehicle for tackling the problem is the UN Framework Convention on Climate Change (UNFCCC), created by the 1992 Rio Summit and now with 196 parties.
Efforts under the UNFCCC are based on two thrusts: reducing carbon emissions (“mitigation”) and shoring up defences for countries at risk (“adaptation”).
But agreeing emissions limits and dividing the burden has bedevilled these hugely complex talks for years.
Curbing emissions carries a cost in energy efficiency and switching out of cheap, plentiful fossil fuels that are the backbone of today’s energy supply.
Rich countries agree they bear historic responsibility for today’s warming. But they say tomorrow’s warming will be caused by developing giants, led by China, the No 1 carbon emitter, which are now voracious fossil-burners.
In 2009, an attempt at a UNFCCC deal at a summit in Copenhagen was a near-fiasco. It was saved by a last-minute plan to limit warming to 2 Celsius over pre-industrial levels and ratchet up aid to vulnerable countries.
Four years of grinding negotiations ensued to frame this goal, which the UN hopes to boost on Tuesday with the New York summit.
The objective is a global pact in Paris at end-2015 that will take effect from 2020.
The draft deal still has huge gaps, and sceptics doubt it will achieve much anyway. They say bilateral, regional or industrial agreements offer a better chance at swift emissions curbs.
