A new report from the United Nations’ (UN) body on the science of climate change, the Inter Governmental Panel on Climate Change (IPCC), has found that the theory of man-made global warming is ’95 per cent likely’.

The first instalment of the IPCC’s Fifth Assessment Report (AR5) was released today (27 September), and claims that ‘warming of the climate system is unequivocal’ and that it is ‘extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century’. According to the IPCC, for an outcome to be ‘extremely likely’, the probability has to sit between 95 and 100 per cent.

This marks the highest IPCC probability rating for man-made climate change yet, up from the 'very likely' (90 per cent) in 2007 and 'likely' (66 per cent) in 2001.

Prepared by the IPCC’s Working Group I at a meeting in Stockholm, AR5 is to be released in four parts between September 2013 and November 2014, and will reportedly be the ‘most comprehensive’ assessment of scientific knowledge on climate change since AR4, in 2007. Indeed, the full report will comprise 2,500 pages of text, draw on ‘millions of observations’ and over ‘two million gigabytes of numerical data from climate model simulations’, and cite over 9,200 scientific publications, more than three quarters of which have been published since the last IPCC assessment.

Report findings

The first instalment suggests that ‘warming of the climate system is unequivocal’, and that since the 1950s, many of the observed changes are ‘unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased’.

It cites that mankind is ‘extremely likely’ to have been responsible for ‘more than half’ of the observed increase in global average surface temperature from 1951 to 2010, as carbon dioxide (CO2) concentrations have increased by 40 per cent since pre-industrial times, ‘primarily from fossil fuel emissions and secondarily from net land use change emissions [such as deforestation]’. Further to inducing a warmer climate, the effect of CO2 emissions has also caused ocean acidification (which threatens marine life), as the ocean has absorbed about ‘30 per cent of the emitted anthropogenic carbon dioxide’.

Additionally, the combination of warmer oceans and reduced ice sheets and glaciers as a result of anthropogenic global warming, will mean that the global mean sea level rises at a ‘faster rate than we have experienced in the last 40 years’. and cause widespread flooding.

The report reads: ‘The total anthropogenic RF [the change in energy flux caused by a driver, calculated at the top of the atmosphere] best estimate for 2011 is 43 per cent higher than that reported in AR4 for the year 2005. This is caused by a combination of continued growth in most greenhouse gas concentrations and improved estimates of RF by aerosols indicating a weaker net cooling effect.’

In terms of the Earth’s surface temperature, the IPCC found that each of the last three decades has been successively warmer than any preceding decade since 1850.

Detailing the physical evidence behind climate change, the report claims its findings are becoming more accurate with better observations, advanced climate models, and an improved understanding of climate system responses.

Using four scenarios, each varying in greenhouse gas concentrations and aerosols, the Working Group I projects possible temperature increases for the early, mid-, and late 21st Century. In all but the lowest scenario, global surface temperature change by the end of the 21st century is projected to exceed 1.5 degress Celsius (°C) relative to 1850 to 1900. For the two highest scenarios, it is likely to exceed 2°C.

The report adds that a possible pause in warming over the past 15 years does not reflect long-term trends. Indeed, it claims that in the Northern Hemisphere, 1983–2012 was ‘likely’ (66-100 per cent) the warmest 30-year period of the last 1400 years.

Effects of CO2 will continue ‘even if emissions stop’

Rajendra Pachauri, Chair of the IPCC, said that the first instalment provides ‘a firm foundation for considerations of the impacts of climate change on human and natural systems and ways to meet the challenge of climate change’. However, these will be among the aspects assessed in the contributions of Working Group II and Working Group III, to be released in March and April 2014.

Speaking on the launch of the first instalment of AR5, Thomas Stocker, one of the Co-Chairs of Working Group I, said: "Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system... Heat waves are very likely to occur more frequently and last longer. As the Earth warms, we expect to see currently wet regions receiving more rainfall, and dry regions receiving less, although there will be exceptions.”

He added: “As a result of our past, present and expected future emissions of CO2, we are committed to climate change, and effects will persist for many centuries even if emissions of CO2 stop… Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions.”

UN Secretary General, Ban Ki-moon congratulated the working group on its report, saying: "Thanks to the dedicated work of a global community of scientists, supported and endorsed by the world’s governments, we know the nature of the problem and the options for addressing it.

"This new report will be essential for governments as they work to finalize an ambitious, legal agreement on climate change in 2015 [at the 2015 UN Climate Conference]... The goal is to generate the political commitment to keep global temperature rise below the agreed two-degree Celsius threshold.

"We need to build resilience and seize the opportunities of a low-carbon future....The heat is on. Now we must act."

Report ‘makes clear what is at stake if we don’t act’

EU Climate Action Commissioner Connie Hedegaard added: ''The issue is not whether to believe in climate change or not. The issue is whether to follow science or not.

"The day when all scientists with 100 per cent certainty warn you against climate change, it will be too late. If your doctor was 95 per cent sure you had a serious disease, you would immediately start looking for the cure. Why should we take bigger risks when it's the health of our planet at stake?"

Hedegaard added that the European Commission will present climate and energy targets for 2020 'before the end of the year'. She added: "Europe will continue to demand more action from all the emitters.

Responding to the panel’s findings, the UK’s Secretary for Energy and Climate Change, Ed Davey, stressed the urgency for action, saying: “The message of this report is clear - the Earth’s climate has warmed over the last century and man-made greenhouse gases have caused much of that global warming. The gases emitted now are accumulating in the atmosphere and so the solutions must be set in motion today. The risks and costs of doing nothing today are so great, only a deeply irresponsible government would be so negligent.

“Without urgent action to cut greenhouse gas emissions this warming will continue, with potentially dangerous impacts upon our societies and economy. This strengthens the case for international leaders to work for an ambitious, legally binding global agreement in 2015 to cut carbon emissions.

“This report is the most authoritative, credible analysis of climate change science ever. It represents a huge amount of work by over 250 unpaid scientific experts drawn from universities and research institutes in 39 different countries around the world. We owe them our gratitude because this report makes clear what is at stake if we don’t act”.

UK must 'accept the folly of grasping for yet more oil and gas'

The UK Government has been criticized in the past for relying too heavily on fossil fuels for its future energy mix, with many lamenting the lack of government action on bringing forward a commitment to decarbonise the energy sector by 2030.

Chief Scientist at Greenpeace, Doug Farr, said: “Dangerous levels of warming of two degrees or more can be avoided, but this requires countries like the UK accepting the folly of grasping for yet more oil and gas in the Arctic, the tar sands and the Home Counties, and instead taking strong and rapid action on renewables.

“Unfortunately, those taking action against climate change by peacefully protesting against oil drilling in the Arctic are currently detained in custody in Russia, while those most responsible – the fossil fuel industry – are courted and protected by governments around the world. It should be the other way around."

The IPCC Fifth Assessment Report cycle concludes with the publication of its Synthesis Report in October 2014.

Read more about the IPCC and the Summary for Policymakers from Working Group I.