Where does the 1.5 °C come from?: A summary of the IPCC special report (SR-1.5)

If some of these terms are new to you, open this article up side by side – we’ve tried to explain some climate jargon!


The publishing of the Intergovernmental Panel on Climate Change’s Special Report on Global Warming of 1.5°C (SR-1.5) on the 8th of October 2018 stands out as a notable watershed moment for climate action: geopolitically and on the grassroots level.

It brought the realities of the Climate and Ecological Emergency into clear focus, laying out the consequences of limiting global heating to 1.5°C as opposed to 2.0°C, and prescribed the scale of action necessary to limit this heating and mitigate the worsening of the damage climate change is already inflicting.

In its wake of that report, climate activism has surged, spearheaded by the Youth Strike for Climate, the Sunrise Movement and Extinction Rebellion; several towns, cities and countries have begun to raise prior climate target ambition as the Overton window shifted into uncharted waters, and decisions previously politically impossible started to be seen as necessary.

What we must not forget is that this information has been reported upon annually, assessing evidence we already have – updated year on year with the latest science, and whilst shocking it was not the first sounding of the alarm.

What is the IPCC?

The IPCC was formed in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP).

Its purpose was to use the latest science to provide the world with an objective understanding of the impacts and risks of anthropogenic climate change and published their first report in 1990 and it served as the basis of the United Nations Framework Convention on Climate Change (UNFCCC), leading to the first conference of the parties (COP) in Berlin in 1995.

Very importantly we must note the “Intergovernmental” element of the IPCC as opposed to “International”, relating to the political nature of its consensus-based decision making – which has effectively resulted in more conservative estimates and reporting.

In her latest book On Fire – the Burning Case for a Green New Deal published in late 2019, Naomi Klein summarises how we got to where we are today despite the IPCC advising governments internationally:

“We have dangerously warmed our world already, and there was a time when many had the right to claim ignorance. For the past three decades, since the intergovernmental panel on climate change was created, and climate negotiations began, this refusal to lower emissions has been accompanied with full awareness of the dangers. This kind of recklessness would be impossible without institutional racism – even if only latent.”

What does the special report (SR-1.5) say?

In SR-1.5, the IPCC recommends that to stay below 1.5°C we must reduce carbon dioxide emissions to zero by 2050 (IPCC, 2018).

To achieve this, emissions would need to be cut – at least, in half by 2030, and then in half again by 2040 before being reduced to zero by 2050 (Figueres and Rivett-Carnac, 2020; Hopkins, 2019) and this is where the often-cited 2030 “deadline” arose from.

For this to be possible, the IPCC states that an “unprecedented societal transformation” is necessary and warned that action must begin immediately. If this is to be done in an equitable and socially just way, industrialised countries and particularly those who benefited from colonial histories would have to drive their emissions down to zero far earlier to enable the Global South and Indigenous North to emit carbon as they transition their own economies to net-zero forms (IPCC, 2018).

A lesser-discussed element of SR-1.5 is that it establishes a carbon budget that gives us a 67% chance of staying below 1.5°C of global heating (Thunberg, 2019).

On the 1st of January 2018, that budget was 420 gigatonnes – which sounds substantial, but we annually emit around 52 gigatonnes (ECOFYS, 2019), meaning that at current rates we would use up that budget in 8 and a half years. Many scientists deem this an overly generous estimation (Bendell, 2019) and in the report itself, it notes that every year of inaction loses us the equivalent of two years to stay below the 1.5°C threshold (IPCC, 2018).

What’s the significance of 1.5°C?

SR-1.5 stresses that a 1.5°C or 2°C global temperature rise would have colossally different magnitudes of impact on people, wildlife, and the natural world (IPCC, 2018).

These increases in impact are in no way linear due to the complexity of natural systems, and the myriad of tipping points, in the Earth’s climate (Figueres and Rivett-Carnac, 2020).

For example, if the planet’s temperature rises to 2°C as opposed to 1.5°C, 37% – 2.6 times more, of the global population would be subjected to extreme heat at least once every five years and maize harvests in the tropics would be 2.3 times worse; we would see twice as many mammals, twice as many vertebrates and three times as many insects go extinct and we would also see an additional 6 centimetres of sea-level rise on average whilst a halving of marine fisheries internationally (IPCC, 2018).

These are just a handful of examples and whilst 0.5°C sounds like a marginal increase, the magnitude of impacts multiplies exponentially should we cross the 1.5°C threshold – as Christina Figueres, one of the key drivers of the Paris Climate Accords sums up:there is no continuity at 1.5°C of global warming”.

It is important to note: more than half of all carbon dioxide emissions in human history were released after that first IPCC assessment report was published in 1990 (IEEP, 2020).

Eloquently put by the author of Future Earth: A Radical Vision for What’s Possible in the Age of Warming, meteorologist and climate correspondent, Eric Holthaus:

“We’ve done more harm to the climate system knowingly than we ever did before scientists’ warnings.”

What next?

The IPCC’s Special Report on Global Warming of 1.5°C represents a wake-up call to humanity.

To act immediately and in collaboration: on scales we have never seen before, to transform our societies and the infrastructures that support them, and to place equity at the heart of actions and decisions with global impacts.

The report emphasises that there is no one silver bullet solution (IPCC, 2018): many man-made and natural solutions to reduce carbon dioxide emissions already exist whilst others are in their infancy – Carbon Capture and Storage, for example, does not exist at a scale proportional to the necessary drawdown efforts (CAT, 2020), so remains a hypothetical solution in society’s repertoire and the roadblock is in fact political and societal, not technological.

Passing that 1.5°C threshold would limit our ability to mitigate catastrophic runaway climate change, inflicting ever-greater impacts upon people, planet, and wildlife (IPCC, 2018).

So, understanding and communicating this context of Climate and Ecological Emergency is crucial and even more so, is transforming that knowledge into action.


Bendell, J. (2019). Doom and Bloom: Adapting to Collapse. In: Extinction Rebellion This Is Not a Drill: An Extinction Rebellion Handbook. Great Britain: Penguin.

CAT (2020). Zero Carbon: Rising to the Climate Emergency. Wales; Centre of Alternative Technology.

Figuerres, C and Rivett-Carnac, T (2020). The Future We Choose: Surviving the Climate Crisis. Great Britain: Manilla Press.

Hopkins, R (2019). From What Is to What If: Unleashing the power of imagination to create the future we want. USA: Chelsea Green Publishing.

Klein, N (2019). On Fire – the Burning Case for a Green New Deal. Canada: Allen Lane

Thunberg, G (2019). No One is Too Small to Make a Difference. London: Penguin.


Author : Scott McAulay

Coordinator of the Anthropocene Architecture School

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