Q. What happened yesterday?
A. THE IPCC published a section of its Fifth Assessment Report (AR5) on climate change. The report will be finalised in 2014.
Q. What is the IPCC?
A. The Inter-governmental Panel on Climate Change was established by the United Nations Environment Programme and the World Meteorological Organisation in 1988. Its job is to provide a "clear scientific view" on the state of knowledge of climate change. It also assesses the potential environmental and socio-economic impacts.
Q. What does this report say?
A. It says the debate is over. The climate system is warming, and many of the changes are unprecedented over decades to millennia.
The atmosphere and oceans have warmed, the amounts of snow and ice have diminished, sea levels have risen and concentrations of greenhouse gases have increased.
The Earth's surface has been successively warmer in each of the past three decades than at any time since 1850.
Q. What does this mean?
A. It means it's time to act. The report raises the probability that most global warming is man-made to 95pc, from 90pc in its 2007 report. "Human influence on the climate system is clear," it says. That means we have to make deep changes in how we live our lives. Unless the problem is tackled, global temperatures will rise between 0.3C and 4.8C up to 2011, Arctic sea ice will continue to shrink and thin, and seas will rise between 26cm and 82cm.
Q. What does it mean for Ireland?
A. More extreme weather events, like the November 2009 rains, which left large parts of the country under water. More storms and more flooding as seas rise, adding to insurance costs and droughts in the summer. Extreme cold could also be a problem, and food production could also be affected.
Further afield, the changes could be more pronounced, including droughts across sub-Saharan Africa and extreme tropical storms. Climate refugees, people fleeing countries because of extreme events, may become a common sight.
Q. So what's next?
The Government has published the heads of a Climate Change Bill, which is likely to go through the Dail next year, but the lack of targets has been criticised.
Q. What needs to happen to prevent dangerous and irreversible climate change?
A. We need to change our behaviour. Walking to the shop instead of taking the car and using public transport would put us on the right path.
The problems in agriculture are more difficult to solve, as Irish farming practice is considered relatively 'green'.
Not burning turf in power stations would also help, as would insulating homes.
Q. But isn't the science discredited? Wasn't there a controversy about the last assessment report?
A. November 2009's 'Climategate' involved leaked emails from the Climatic Research Unit (CRU) at the University of East Anglia, one of many data sources used in AR4. The mails suggested scientists manipulated data and attempted to suppress critics.
The CRU said the mails had been taken out of context and merely reflected an honest exchange of ideas.
The university, and subsequent investigations, found no evidence of wrongdoing.
Q. What happens now?
A. The UN will host a meeting of world leaders and governments in September next year, and aims to have a global, legally binding agreement among all nations by 2015 to set out clear targets, priorities and ways of reducing emissions.
Among the stumbling blocks is the attitude of some developing nations, which believe that western countries should contribute more. Getting them on board will be key. That process begins in November, when governments including Ireland meet at the 19th session of the Conference of the Parties to the UNFCCC (United Nations Framework Convention on Climate Change) in Poland.