[Charts] What is the 1.5°C ‘target’?

There’s an important number in the world of climate change jargon that scientists and politicians have warned not to cross. Foreboding headlines say we are getting closer and closer to permanently crossing this threshold, beyond which the effects of global warming on weather patterns will likely grow stronger. That threshold is considered to be 1.5 degrees Celsius (1.5°C).

According to U.S. and European climate service agencies, 2023 was the hottest year on record and the 1.5°C threshold was temporarily breached over the last 12-months period, from February 2023 to January 2024. But what exactly are the origins of this threshold, why does it inspire urgency and what might happen if it’s crossed?

Global warming on the rise

Anthropogenic (human-induced) global warming has steadily pushed the earth’s surface temperatures progressively higher. Greenhouse gasses released from industrial activity get trapped in the atmosphere and cause the earth’s surface to warm up as a result. While plenty of natural processes also emit greenhouse gasses, anthropogenic activities are overwhelmingly driving global warming today, and doing so more rapidly than ever before. Carbon dioxide is the most ubiquitous of these greenhouse gasses, lasting in the atmosphere for between 300 to 1000 years.

According to the Intergovernmental Panel on Climate Change (IPCC), the earth’s surface temperature has risen by 1.1°C since pre-industrial times (generally counted from the year 1850 or 1900 onwards). At 1.1°C, extreme weather events like droughts, rainfall, and heatwaves, among others, have become more frequent. At 1.5°C or higher, the duration, frequency and intensity of these events are likely be even higher, and could challenge the adaptability of ecosystems, settlements, and humans.

A political target

The target to limit global warming to 1.5°C by the end of the century, however, is the lower end of a temperature range that was politically negotiated and set by countries at the 21st Conference of Parties (COP21) in Paris, in 2015. “It is not a scientific number based on a physical threshold as such,” said Raghu Murtugudde, Professor of Climate Studies at the Indian Institute of Technology Bombay and Professor Emeritus at the University of Maryland. “If we cross 1.5 degrees, we will continue to experience what we are experiencing today.”

Enshrined in the Paris Agreement, each member state agreed to “holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change.”

The IPCC released its Special Report on limiting global warming to 1.5 C after the Paris Agreement was signed and on the request of the United Nations Framework Convention on Climate Change. This, some researchers have said, is what “led to 1.5 becoming a boundary object” shared by the policy and scientific communities. According to the IPCC’s report, at 1.5 degrees of warming, mean temperatures in land and ocean regions will rise, as will hot extremes, heavy precipitation, and the probability of drought and precipitation deficits in some regions.

But consensus on whether the 1.5°C target should continue to be the “north star” guiding global climate action is split, given that, by most estimates, it will be breached in the coming decades. The latest global carbon budget report says that the remaining carbon emissions left to stay within the 1.5°C limit will be exhausted within the next seven years if emissions continue as usual.

An outsized focus on crossing 1.5°C also does not help prepare for impacts at a more localised scale, says Murtugudde. “We only know that at a higher temperature, extreme events will be more intense and frequent. But this information is not very useful because it does not tell us where,” he said, adding, “End of century projections also do not help anticipate or measure local risk factors. We need to see what local risks emerge at any given temperature rise. That means improving our data sets and modelling at decadal intervals, so we are better prepared for impacts at district and city level scales.”

Temporary breach versus a permanent one

Reports of temperatures reaching the 1.5°C mark over the last year have intensified focus on the long-term goals in the Paris Agreement. While the mean surface temperature rise in the context of the Paris Agreement is measured over decades, the temporary breach that occurred this year was of the mean over the last 12 months.

Each month since July 2023 reached record breaking levels of heat, with 2023 replacing 2016 as the warmest on record. This wasn’t the doing of global warming alone – among the major contributors to this unusual spike was the El Nino effect. An El Nino a natural climatic phenomenon in which the sea surface temperatures of the eastern tropical Pacific Ocean become unusually warm. This causes, as Murtugudde puts it, a “mini global warming effect.” The last hottest year on record, 2016, was also an El Nino year.

“The El Nino superimposes on global warming, so the effect is even stronger,” Murtugudde explained.

Even as global warming approaches 1.5°C, climate change shouldn’t casually be attributed to every extreme weather event, scientists say. The recent wildfires in Chile, for example, were not found to be made more likely due to the effects of climate change.

Read more: As heatwaves projected to worsen across India, do vulnerability assessments and heat action plans suffice?

Banner image: Construction workers in Iran. Photo by Mostafameraji/Wikimedia Commons.