QUICK & PULSE

A new study by James Hansen, the first to sound the alarms of the climate crisis in the 1980s, indicates that the speed of climate change has been underestimated

From OC – In 1988, the American James Hansen was the first scientist to affirm that global warming was a reality. Now, the retired NASA researcher maintains that even the least ambitious target of the Paris Agreement, to limit global warming to 2°C above pre-industrial levels, would already be a lost cause. In a new study, published last Monday (3/2) in the scientific journal Environment: Science and Policy for Sustainable Development, Hansen and colleagues assert that science has underestimated the pace of warming – and that we will see its most deleterious effects even sooner than science had expected.

“The 2°C target is dead,” Hansen stated in a press conference following the release of the research. According to the article, the 2°C limit may be exceeded as early as 2045. Moreover, fundamental ocean current systems essential for climate regulation – such as the Atlantic Meridional Overturning Circulation (AMOC) – may collapse within 20 or 30 years, leading to a rise in sea levels by “several meters” and the global climate system to a point of no return.

The new research reinforces a line of investigation followed by Hansen over the past few years. One of the main voices in the so-called “accelerationist” current of climate science, the scientist maintains that since 2010, the rate of global warming has increased dramatically, as a result of the intensification of the planet's energy imbalance. At the root of the acceleration would be the reduction of aerosol pollution – particles that, when concentrated in the atmosphere, help cool the planet.

The hypothesis that global warming has accelerated in recent years is supported by prominent researchers in the field, but it is far from a consensus: the so-called "traditionalist" group, also composed of renowned researchers, argues that despite the impacts exceeding the predicted ones, there is no evidence of a recent acceleration in global warming – which would be following the trend of the last few decades.

In the new research, Hansen and colleagues claim that the cooling effect of aerosols has been underestimated by scientists (including those from the IPCC, the UN scientific body for climate), masking the true pace of climate change. Deepening the conclusions of a previous article, the team of scientists led by Hansen points out that the accumulation of greenhouse gases in the atmosphere produces more warming and in less time than was known, which only became perceptible when aerosol pollution was controlled.

The science has already widely recognized that aerosol pollution – which brings serious complications for human health – paradoxically helps control the planet's warming by reflecting solar radiation back into space and thus reducing the incidence of heat. What the new research points out is that the weight of this compensation is much greater than that pointed out by the IPCC, and that the reduction of this pollution is at the root of the deepening energy imbalance of the Earth, being the main driver of the acceleration of global warming.

"In this article, we conclude that the estimate of the climatic forcing of aerosols by the United Nations scientific advisory body, the Intergovernmental Panel on Climate Change (IPCC), is underestimated," says the article.

The image shows the intensification of the planet's warming rate: the purple line indicates the anomaly rate from 2010 and the green, the rate recorded from 1970 to 2010.

“The underestimation of the aerosol forcing resulted in an underestimation of climate sensitivity. This dual impact helps explain the acceleration of global warming and alters future climate projections, increasing the risk of intergenerational injustice,” the authors conclude. Climate sensitivity at equilibrium (ECS, in English abbreviation) is an estimate of how much the Earth's temperature would rise if the concentration of CO2 in the atmosphere doubled. According to the research, the planet's climate is more susceptible to the increase in greenhouse gas concentrations than admitted by the IPCC, which translates into more severe impacts.

Among the main climate impacts, with consequences that may render the future of new generations unsustainable, are the definitive collapse of the Paris Agreement target and the collapse of one of the main ocean currents responsible for global climate regulation.

Researchers highlight that the increase of 0.4°C in global temperature during the 2023-2024 El-Niño event represents a much greater warming than observed in more intense versions of the atmospheric-oceanic phenomenon. This means that the known rate of global warming and El-Niño alone do not explain the magnitude of the observed warming, reinforcing the hypothesis of acceleration.

"We found that a large part of this additional warming was caused by the reduction of aerosol emissions from ships, a measure implemented in 2020 by the International Maritime Organization to combat the effects of atmospheric pollutants on human health," explain the authors.

Therefore, even with the arrival of La Niña – a phenomenon that, unlike El Niño, tends to cool the planet – the trend is that temperatures will continue to be close to the records reached in 2024, as confirmed by the temperature data from January 2025. “We expect the global temperature not to fall much below the level of 1.5°C of warming, fluctuating around or above this value in the coming years, which will help confirm our interpretation of the sudden global warming,” the article says.

Projections indicate that high sea surface temperatures and the increase of “hotspots” in the oceans will continue, extending coral bleaching and impacts to other forms of marine life. Moreover, the increase in sea surface temperature and the warmer atmosphere will drive more powerful tropical storms, tornadoes, and intense storms – and consequently, more extreme floods. The increase in global temperature will also intensify more intense heatwaves and droughts, including so-called “droughts-lightning,” which develop rapidly even in regions with normal average precipitation levels.

The greatest long-term impact on humanity will, however, come from changes in the polar regions. Hansen and colleagues suggest that the melting of polar ice and the injection of fresh water into the North Atlantic Ocean are more intense than indicated by previous estimates. This could result in the collapse of the AMOC, the ocean current that transports warm water from the tropics to the North Atlantic and has a strong influence on the climate, in 20 or 30 years.

“The collapse of the AMOC will trigger irreversible problems, including the rise of sea levels by several meters – that's why we describe the collapse of the AMOC as the ‘point of no return’ for the climate”, say the scientists, who advocate for more efforts to investigate the consequences of the failure of the ocean current. In 2023, another study pointed out that this collapse would also have irreversible consequences for food security, causing the loss of half of the global area for wheat and corn cultivation.”

The study predicts that the planet should expect a warming of 0.2°C to 0.3°C per decade over the next 20 years, which would lead to a global temperature 2°C above pre-industrial levels by 2045, burying the Paris Agreement target.

The projected rate of warming could slow down if the growth rate of greenhouse gases decreased, but there is no evidence that this is happening. The main factor driving the ongoing climate change is the increase in greenhouse gas concentrations, mainly CO₂, but also CH₄ (methane) and N₂O (nitrous oxide). The climatic forcing caused by the increase of these gases is an essential indicator, showing that there has been no progress in reducing the growth rate of the climatic forcing of greenhouse gases, the article points out.

With the increasing demand for energy from fossil fuels, researchers consider it "implausible" to contain warming to 2°C. Therefore, they propose in the article the adoption of "deliberate cooling actions." In other words: the famous and controversial measures of geoengineering, which have unpredictable effects and encounter resistance from a large part of climate scientists precisely due to the unknown nature of their side effects. (LEILA SALIM)