Temperatures Are Rising Faster than Expected
Recent research indicates that global warming has accelerated significantly since 2010, with temperatures rising more than 50% faster than the 1970-2010 average of 0.18°C per decade.
It has been long known that sunlight is constantly being reflected back into space by clouds, snow, aerosols, and ice - effectively cooling the atmosphere or slowing and compensating for the warming caused by the greenhouse effect.
While the greenhouse effect traps the energy from sunlight into the atmosphere and cause average atmospheric temperatures to rise due to accumulating energy, the cooling results from energy being reflected back to space before being trapped.
According to this research, recent and ongoing reductions in aerosol emissions from shipping are leading to an acceleration of global warming - essentially by reversing this cooling.
As regulations have curtailed aerosol pollution, particularly in the shipping industry, this masking effect has diminished, revealing the full force of greenhouse gas-driven warming.
In other terms, while there are benefits to reducing aerosols in the atmosphere, this study shows that it's equivalent to removing the brakes on global warming.Â
Why Are We Learning About This Now?
The Intergovernmental Panel on Climate Change (IPCC) has long recognised the role of aerosols in climate change. Aerosols, including sulphate, nitrate, ammonium, and carbonaceous particles, can cool the climate by scattering sunlight and causing clouds to also reflect more sunlight.
While the IPCC acknowledges the importance of aerosols, the new findings suggest that its climate models may have underestimated their cooling effect. This discrepancy between observed temperature increases and model projections suggests that current climate models might not fully capture the complexities of aerosol interactions or the speed at which these changes are occurring.
One key reason for this underestimation lies in how aerosols were previously measured and incorporated into climate models. Historically, the cooling effect of aerosols has been difficult to quantify because aerosols have complex, short-lived interactions with clouds and radiation.
Many models assumed a lower cooling effect because of uncertainties in the measurement of aerosol-cloud interactions. The new study, however, uses updated satellite data and observational analysis to show that the cooling impact of aerosols was stronger than previously thought.
Another reason is that climate models used by the IPCC often prioritise long-term greenhouse gas-driven trends, meaning that short-term but significant cooling effects of aerosols may not have been fully accounted for.
Since aerosols have been rapidly removed due to stricter pollution controls, warming has intensified more quickly than expected, revealing gaps in existing models.
Another point of divergence concerns sea-ice-atmosphere interactions. The study suggests that models may have underestimated how reductions in aerosols influence cloud cover and sea ice melt.
As ice melts, less sunlight is reflected back into space, exacerbating warming further—a process known as ice-albedo feedback. If climate models do not fully capture the speed of this feedback loop, they may miscalculate the rate of warming and its cascading effects.
How Did This Study Uncover These Effects?
This study arrived at its conclusions by analysing new satellite observations and real-world temperature data rather than relying solely on existing climate models.
The authors examined how recent reductions in aerosol emissions correlated with rapid temperature increases, particularly in regions where shipping activity had previously contributed significant aerosol pollution.
The direct relationship between declining aerosols and rising temperatures provided strong evidence that previous models had underestimated this effect.
The study also leveraged advanced climate reanalysis techniques, which incorporate observational data into climate models to improve accuracy.
By comparing projected temperature trends with actual temperature records, researchers were able to highlight discrepancies and reveal that the cooling effect of aerosols had been stronger than previously assumed.
Another key factor was the improved understanding of aerosol-cloud interactions. Previous models struggled to capture the full extent of how aerosols modify cloud properties, particularly their ability to make clouds more reflective.
The study used refined cloud microphysics data to show that aerosols had been playing a more significant role in cooling the climate than earlier estimates suggested. As a result, the removal of these aerosols due to pollution regulations has had a more pronounced warming impact than anticipated.
What Are the Consequences for the World?
The implications of this accelerated warming are profound. Renowned climate scientist Professor James Hansen has declared the international 2°C climate change target "dead," emphasising that global temperatures could reach this threshold by 2045 unless countered by interventions such as solar geoengineering.
He warns of more severe future scenarios, including extreme weather events and potential tipping points like the collapse of Atlantic ocean currents (AMOC).
If AMOC were to shut down, it could disrupt global climate patterns, leading to more frequent and intense storms, shifts in monsoon patterns, and severe disruptions to agriculture - for example, some studies show that arable land in the UK could drop from around 30% to 7%.
In addition to the risks posed by AMOC collapse, the acceleration of ice melt presents another serious challenge. If Antarctic and Greenland ice sheets continue to destabilise at an increasing rate, sea level rise could exceed current projections, leading to widespread coastal inundation.
The combination of rapid warming, ice melt, and potential ocean current disruption underscores the urgency of reassessing climate models and policies to better align with these emerging threats.
What Policies Should Be Developed in Response?
Given the findings of this study, policymakers face difficult choices about how to address both greenhouse gas emissions and aerosol reductions. While reducing aerosols is crucial for public health - since air pollution causes millions of premature deaths annually - it has also removed a temporary buffer against warming.
This means that emission reduction strategies must be even more aggressive to compensate for the lost cooling effect.
Hansen and other scientists suggest several approaches to mitigate these challenges. One potential solution is the implementation of a global carbon fee and dividend system, which would put a price on carbon emissions and redistribute revenue to citizens, incentivising reductions in fossil fuel use.
Another recommendation is expanding investment in nuclear power, which can provide reliable, low-carbon energy without the intermittency challenges of wind and solar power.
Finally, there is growing debate around geoengineering solutions, such as stratospheric aerosol injection, which would involve deliberately introducing particles into the atmosphere to reflect sunlight and counteract warming.
The Need for Reevaluation of Climate Policies
These observations underscore the urgency of re-evaluating current climate policies and models. The potential underestimation of aerosol impacts suggests that achieving the goals set by international agreements, such as the Paris Agreement's aim to limit warming to 1.5°C, may be more challenging than previously thought.
The recent acceleration in global warming due to reduced aerosol emissions from shipping presents a critical challenge to existing climate models and policies. Addressing this issue requires a multifaceted approach, including revisiting climate models to better account for aerosol impacts, implementing robust emission reduction strategies, and exploring innovative solutions to mitigate the accelerating warming trend. The world cannot afford to be complacent.