1.5°C versus 2°C of Warming: Political Histories and the Climate Implications

by Jack Johnson

Greenhouse gas emissions due to human activity raise the atmospheric temperature above the long-term global average. Emissions have already warmed the planet by 1.1°C-1.3°C above pre-industrial levels [1]. To curb the severe damages caused by our changing climate, clear climate targets are necessary. Devising climate policies without a clear warming target would be akin to asking a pilot to land a plane while blindfolded. Commonly accepted climate targets enable us to gauge what needs to be done to avoid runaway climate breakdown. 

While policy makers and scientists alike deemed 6°C warming catastrophic, 2°C above pre-industrial levels has long been identified as an acceptable threshold guiding climate policy [2]. However, anyone with a keen understanding of climate policy would comment that in recent years, 1.5°C has also been included in the Copenhagen Accord (2009), the Paris Agreement (2015), and the Glasgow Climate Pact (2021)

So, why are there two separate climate targets used for global climate policy, and what do they mean in relation to climate impact?

Historical background to 1.5°C and 2°C climate warming limits

The history of 2°C

In 1990 the Stockholm Environmental Institute (SEI) began investigating climate limits and tipping points [3]. Their 1991 report concluded that 2°C above pre-industrial levels was the threshold, below which global warming needed to remain, to avoid the worst impacts of climate change [3]. In the following years, the SEI’s report began to permeate into the political agenda and public discourse.

In 1996, the European Union became the first political body to acknowledge the need to stay below 2°C [3]. 2°C was a compromise between political-economic objectives and potentially irreversible environmental damage caused by unabated emissions. The temperature goal continued to gain traction in environmental circles during the following years. Greenpeace latched on to the target in the 1990s, and the G8 meeting in 2005 made reference to the temperature goal [2,4]. While climate policy remained complex, the ultimate goal was clear: limit warming to 2°C. 

As the Intergovernmental Panel on Climate Change’s (IPCC) third (2001) and fourth (2007) assessment reports provided stronger scientific backing of the 2°C target, it was officially adopted by the United Nations in 2009 under the Copenhagen Accord ? the outcome of the 15th Conference of the Parties (COP15) [5,6]. With a concrete target of 2°C, the Copenhagen Accord also stated that Parties would ‘consider’ limiting temperature below to 1.5°C [7]. 

Why a second target, and where did it come from?

The rise of 1.5°C

The 1.5°C target is rooted in years of political groundwork and scientific research. In 2008, the Association of Small Island States (AOSIS) commissioned a report from the Potsdam Institute for Climate Impact Research on the impacts of 2°C [7]. The report was clear that even 2°C, akin to higher warming scenarios, would spell disaster for many island states [7]. For example, it is estimated that at 2°C warming, a majority of the Marshall Islands’ land area would be submerged underwater by 2100 [8].  As 2°C became an indefensible goal for the most vulnerable nations, AOSIS adopted a new climate target of limiting warming well below 1.5°C [7].

AOSIS countries arrived at COP15 in Copenhagen with 1.5°C as a ‘non-negotiable’ target [9]. Despite their efforts, industrialized nations resisted the more ambitious target on the basis that it was a politically unrealistic objective [7]. The accord paid scant attention to 1.5°C and instead determined 2°C as the globally accepted climate target. The most climate-vulnerable countries left COP15 defeated. Lumuandi Di-Aping, the then head of the G77 group of 130 poorest nations said the Copenhagen Accord was ‘a suicide pact’ for the world’s most vulnerable countries [10]. This however was only the start of the political struggle to recognize 1.5°C.

Following COP15, AOSIS, African states, and leading NGOs continued to make the case for the more ambitious climate target [7]. Their activism was backed by a growing body of scientific research which supported the 1.5°C target [9] . 

The next political milestone for the 1.5°C target was the 21st COP (COP21) in 2015. In Paris, the coalition of counties who supported the 1.5°C target had grown to 106 countries ? a majority of Parties to the United Nations Framework Convention on Climate Change (UNFCCC) [7]. Nonetheless, the will of the largest polluters won again as the Paris Agreement identified 2°C as a strict temperature limit, and 1.5°C as a mere aspirational temperature goal [12]. Still, COP21 was a sign that 1.5°C had shifted from being an ‘unrealistic’ goal to a widely supported target [7]. 

Scientific comparison of 1.5°C and 2°C climate warming limits

Most recently, the IPCC’s 2018 Special Report on Global Warming of 1.5°C provided a significant boost to the emerging climate objective. The report, published by the world’s premier climate science body, compared the impacts of reaching 1.5°C versus 2°C [13]. The findings were staggering. A summary of just a few of the findings include:

  • At 2°C, 1.3 billion more people will be exposed to extreme heat waves, 61 million more exposed to drought, and 10 million more displaced due to sea level rise relative to 1.5°C [14,15]. 
  • At 2°C, sea-ice-free summers in the Arctic will happen every 10 year, compared to every 100 years at 1.5°C [16]. 
  • At 2°C, 8% of vertebrates, and 16% of plants will lose more than half of their ranges. At 1.5°C, these proportions are reduced by half [16].

The 2018 report made clear that 2°C had become a political target for wealthy nations. 1.5°C became the only legitimate climate target for countries genuinely concerned about tackling the climate crisis. 

Climate targets moving forwards

Since the IPCC’s report in 2018, 1.5°C has increasingly become the global climate target. However, while the recent Glasgow Climate Pact ‘resolves’ to pursue 1.5°C, it also ‘reaffirms’ the Paris Agreement’s identification of 2°C as a hard warming limit [17]. The continued inclusion of 2°C as an acceptable target allows for the most polluting countries to renege on their obligation to take stronger climate action. With warming already at 1.1°C-1.3°C, all countries, organisations, and individuals must immediately shift their gaze to 1.5°C, leaving 2°C behind [1]. 

Featured Image Courtesy of UNFCCC Flickr


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[2] Tschakert, P. (2015), ‘1.5°C or 2°C: a conduit’s view from the science-policy interface at COP20 in Lima, Peru’, Climate Change Responses, 2(3) Available at: https://climatechangeresponses.biomedcentral.com/articles/10.1186/s40665-015-0010-z <accessed 09 December 2021>.
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[8] Mulhern, O. (2020), Sea level Rise Projection Map – Marshall Islands’, Earth, Available at: ‘https://earth.org/data_visualization/sea-level-rise-by-2100-marshall-islands/ <accessed 09 December 2021>.
[9] Mathiesen, K. (2014), ‘Defining moments in climate change: hope and crisis in Copenhagen’, The Guardian, Available at: ’https://www.theguardian.com/global-development-professionals-network/2014/apr/07/copenhagen-climate-change-paris-talks <accessed 09 December 2021>.
[10] Vidal, J. (2009), ‘Vulnerable nations at Copenhagen summit reject 2°C target’, The Guardian, Available at: https://www.theguardian.com/environment/2009/dec/10/copenhagen-climate-change <accessed 09 December 2021>.
[11] United Nations Framework Convention on Climate Change (2015), ‘Report on the structured expert dialogue on the 2013-2015 review’, Available at: https://unfccc.int/resource/docs/2015/sb/eng/inf01.pdf <accessed 09 December 2021>.
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[14] World Wildlife Fund, ‘The Urgency of 1.5°C’ Available at: https://wwf.panda.org/discover/our_focus/climate_and_energy_practice/ipcc152/ <accessed 09 December 2021>.
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[16] Levin, K. (2018), ‘Half a Degree and a World Apart: The Difference in Climate Impacts Between 1.5?C and 2?C of Warming’, World Resource Institute, Available at: https://www.wri.org/insights/half-degree-and-world-apart-difference-climate-impacts-between-15c-and-2c-warming <accessed 09 December 2021>.
[17] United Nations Framework Convention on Climate Change (2021), ‘Conference of the Parties serving as the meeting of the Parties to the Paris Agreement’, Available at: https://unfccc.int/sites/default/files/resource/cma2021_L16_adv.pdf <accessed 09 December 2021>.
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