1.5°C: what it means and why it matters | United Nations

The Urgency of Limiting Global Warming: A Report on Sustainable Development Goals

Introduction

The science is clear: to avert the worst impacts of climate change and preserve a liveable planet, global warming needs to be limited as much as possible and as a matter of urgency. (IPCC)

The Paris Agreement

Under the Paris Agreement, countries agreed to substantially reduce global greenhouse gas emissions to enable the long-term global average surface temperature increase to be kept well below 2°C above pre-industrial levels and pursue efforts to limit it to 1.5°C.(Paris Agreement)

Emphasis on Limiting Global Warming to 1.5°C

At COPs 26, 27, and 28, countries emphasized that the impacts of climate change would be much lower at a temperature increase of 1.5°C, compared with 2°C, and expressed their firm resolve to pursue efforts to limit global warming to 1.5°C.(COP outcomes; IPCC)

Monthly and Annual Breaches of 1.5°C

Monthly and annual breaches of 1.5°C do not mean that the world has failed to achieve the Paris Agreement’s temperature goal, which refers to a long-term temperature increase over decades, not individual months or years. Temperatures for any single month or year fluctuate due to natural variability, including El Niño/La Niña and volcanic eruptions. Consequently, long-term temperature changes are typically considered on decadal timescales. (WMO)

Early Signs of Exceeding the Long-Term Limit

Nevertheless, breaches of 1.5°C for a month or a year are early signs of getting perilously close to exceeding the long-term limit, and serve as clarion calls for increasing ambition and accelerating action in this critical decade. (UNEP).

Global Temperature Changes and Historical Baseline

Global temperature changes are typically measured against the average temperature over a historical, pre-industrial baseline of 1850–1900. This baseline is the earliest period for which high-quality observations of surface temperatures over the land and ocean are available. (IPCC).

Temperature Anomalies and Exceeding 1.5°C

The first months with an average temperature that was more than 1.5°C above the pre-industrial average occurred during 2015-16, driven by both human-caused climate change and a strong, naturally occurring El Niño. The latter part of 2023 and early 2024 also experienced monthly average global temperature anomalies above 1.5°C. (WMO)

First 12-Month Period to Exceed 1.5°C

The first 12-month period to exceed 1.5°C as an average was February 2023 – January 2024, boosted by El Niño, when the average temperature worldwide was estimated to be 1.52°C higher than 1850–1900, according to one scientific dataset (Copernicus Climate Change Service). The likelihood of the annual average global temperature exceeding 1.5°C above pre-industrial levels for at least one year over the coming five years has increased significantly since 2015, when it was close to zero (WMO).

Current Global Warming Trends

The global average temperature for the most recent 10-year period, from 2014 to 2023, is estimated to be the warmest 10-year period on record, at around 1.2°C above the 1850-1900 average (WMO). The 20-year average warming for 2001–2020 relative to 1850–1900 is 0.99°C (IPCC).

Importance of Every Fraction of a Degree

Every fraction of a degree of warming matters. With every additional increment of global warming, changes in extremes and risks become larger. For example, every additional 0.1°C of global warming causes clearly discernible increases in the intensity and frequency of temperature and precipitation extremes, as well as agricultural and ecological droughts in some regions. (IPCC)

Risks and Impacts of Exceeding 1.5°C

Limiting global warming to below 1.5°C will significantly reduce the risks, adverse impacts, and related losses and damages from climate change. Failing to do so will lead to increasingly frequent and dangerous extreme weather events including heatwaves, droughts, wildfires, and heavy precipitation and flooding (IPCC). Extreme heat causes the greatest mortality of all extreme weather, with an estimated 489,000 heat-related deaths per year between 2000 and 2019 (un.org

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