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1.5 Degrees of Paris Climate Agreement

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The international treaty to address climate change, known as the Paris Agreement, will enter into force this year with the news that the EU has joined the US, China, India and dozens of other countries in ratifying.  This is sooner than anyone imagined when the deal was struck last December and gives the world hope that global leaders are serious about dealing with the climate challenge.

The Paris Agreement represents the first time that all countries have agreed that they will act together, as well as nationally, to limit the rise in global temperatures – but what does this mean and is it good news?

Why should we care about global temperatures?

Climate change is happening now.  When we burn fossil fuels, especially coal, for energy, or use our land unsustainably, we pollute the atmosphere with greenhouse gases which subsequently drive temperatures higher.  This in turn leads to many of the climate change impacts already being seen around the world, such as those from prolonged heat waves and drought.  In the UK increased flood risk is one of the greatest climate change related threats.

The Earth’s average temperature has changed naturally before.  However, human civilisation developed during a remarkably stable period of temperatures and now our actions are taking us beyond this.

An introduction to temperature limits

For many years 2°C of warming was the main limit discussed internationally; but as knowledge of climate change impacts developed we came to understand that this was not good enough.

The phrase “1.5 to stay alive” was coined following the realisation that many vulnerable countries’ and low-lying countries’ (such as the Marshall Islands, Tuvalu and Kiribati) very existence is threatened by climate change.  They made inclusion of a 1.5°C limit a deal-breaker at the UN climate summit in 2015; and in the resulting Paris Agreement countries state their commitment to:

“[Hold] the increase in the global average temperature to well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognising that this would significantly reduce the risks and impacts of climate change.”

1.5°C is not just a number, it is the difference between safety and crisis for many – particularly the most vulnerable.  Although temperature limits are informed by science they are political targets in that they serve as a simple substitute for what countries have agreed would lead to an unacceptable risk for a variety of climate impacts.

What difference does half-a-degree make?

Half-a-degree may not sound significant but it does make a huge difference.  For example, there are some substantially bigger impacts projected at 1.5°C and 2°C of global warming – including in extreme weather events, water availability, agricultural yields, sea-level rise and risk to coral reefs.  A recent study suggests that half-a-degree less warming means:

  • 10cm less sea-level rise by the end of the century;
  • Shorter tropical heat waves; and
  • Some hope that some coral reefs could still survive.

When it comes to adapting to the impacts of climate change (‘adaptation’) we should prepare for the worst – so the half-a-degree between 1.5°C and 2°C may not change priorities but will see half-a-degree of additional impacts – we must invest in improving resilience to impacts of higher possible temperatures of 3-4°C or more warming.

Carbon Brief Infographic Carbon Brief infographic

With regards to stopping that extra half-a-degree (‘mitigation’) it is a lot more difficult.  The Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report has only a limited number of scenarios consistent with limiting warming to 1.5°C.  They are more consistent with keeping warming to 2°C or just below and they include substantial cuts in anthropogenic greenhouse gas emissions by mid-century through large-scale changes in energy systems and potentially land use; basically meaning that even to keep warming below 2°C will already require massive changes in the way we generate energy and use land.

Is it still possible to keep temperature rise below 1.5°C?

Annual global average temperature rose to a record 1°C above pre-industrial levels in 2015.  This year is projected to be even hotter – mainly due to climate change, but also boosted by the remnants of the El Niño in the first part of the year.

It is undeniably challenging to keep warming below 2°C, much more to 1.5°C.  We are committed to more surface warming due to the thermal inertial in the Earth’s system from heat stored in the ocean, which means that  even if we could stop emissions today without damaging the global economy, temperatures will continue to rise by a few tenths of a degree over the coming decades.

The IPCC shows a near linear relationship between the sum of all the historical greenhouse gas emissions and global average temperature rise – this gives a remaining global carbon budget of around 1,000 billion tonnes after 2011 to limit warming to 2°C.  At current annual emission rates this budget would last only around 25 years.  And we have only a decade or so at current rates until will have committed the Earth to more than 1.5°C of warming.

Cutting emissions and more

For us to keep the Earth’s temperature to 1.5°C requires deep cuts in emissions and a global transformation in all economic sectors.  There are actions we can take now – such as rapidly phasing out the use of fossil fuels (coal faster but also oil and gas) and replacing these with 100 per cent clean renewable energy (such as solar and wind) by mid-century.  There is also great potential to cut emissions by using less energy and improving energy efficiency, and from other demand-side measures such as shifting diets, transport modes and improving waste management and recycling.

However, cutting emissions might not be enough and most studies suggest we’ll also need to remove carbon dioxide (CO2) from the atmosphere.  Plants do this naturally, so activities such as afforestation and reforestation will be important to suck up and store CO2.  Some people suggest that we may also need large-scale use of unconventional negative emission technologies or ‘geoengineering’ options, which aim to capture large amounts of CO2 and turn it into products or store it underground, rather than have it stay in the atmosphere.  A recent studyshowed that there is no single negative emissions technology, or combination thereof, currently available that could be implemented to meet a below 2°C target without causing significant impact; it went on to say that these impacts could be on land, energy, water, nutrient, albedo or cost, and so our ‘plan A’ must be to immediately and aggressively reduce greenhouse gas emissions.

Negative emissions technologies are generally untested and our understanding of them is in its infancy – so we have to research them more but should recognise that a future hope of extracting vast quantities of CO2 from the atmosphere must not be an excuse to continue to pollute.  Rather, any future use of negative emissions should be to lower the risks associated with higher temperatures.  We should try to prevent emissions now rather than remove them later.

What is the latest science?

The IPCC is preparing a special report on the impacts of global warming of 1.5ºC above pre-industrial levels and related global greenhouse gas emission pathways  for release in September 2018 which will improve our understanding of the implications of a 1.5°C limit.  This is driving research and the 1.5 degrees conference in Oxford with 300 scientists last month showcased this – my takeaways were:

  • Limiting global temperature rise to 1.5°C is technically feasible but extremely difficult. There are reasons to be optimistic – the renewables revolution is coming, with costs of wind and solar down a lot meaning they can out-compete fossil technology; but there are also reasons to be cautious as there are difficult sectors to deal with (aviation and shipping, agriculture, space heating etc.).
  • Sustainable consumption really matters and needs to be talked about more.
  • There are many issues with emissions pathways which ‘overshoot’ 1.5°C and then rely on extensive future use of negative emissions to bring temperatures back down: How high above 1.5°C can you overshoot?  For how many decades can you be above the limit?  Should we rely so much on untested technology which has potential side-effects?  Can wildlife and ecosystem that is able to adapt to higher temperatures adapt again if they come back down?

Higher temperatures lead to greater risk of dangerous climate change impacts and a 1.5°C world will already pose many more dangerous impacts than we are experiencing today.  While better than 2°C, a rise of 1.5°C will still result in large and disruptive climate impacts which will negatively affect particularly poor and vulnerable communities, as well as already fragile ecosystems.

The Oxford conference reinforced the need for dramatic cuts in greenhouse gas emissions to give any chance of limiting warming to below 1.5°C.  But it is not just about cutting emissions – avoiding emissions, through lifestyle choices and energy efficiency, is also important.

WWF has long supported a 1.5°C limit and we, like many others, need to better understand the developing science and the implications to our goal of a world where people and nature thrive.  Limiting the temperature rise won’t be easy and it won’t happen without sustained effort from governments, businesses, civil society and general public.  We don’t know it all, but we know enough to act.

Dr Stephen Cornelius is the Chief Advisor- Climate Change for WWF-UK. He is based in Woking.  


The world took steps to make #ParisAgreement a reality, now we must act to make a 1.5°C world one too:

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