The climate crisis, driven by greenhouse gases, is one of the most defining features of life in the 21st century. This is evidenced by the fact that while 2025 is unlikely to be the warmest year on record – as 2023 was and 2024 will be – it will still be most likely warmer than any year in previous decades. Worryingly, 2025 will also be one of the coldest years in the coming decades. Despite progress in reducing emissions in many countries, temperatures will continue to rise until the accumulated amount of emissions stabilizes.

If the current trend of rising temperatures is not stopped, the consequences are dire. Four to five more decades of rising temperatures are expected, leading to more deadly heat waves in places that have never experienced them before, and even more deadly heat waves in areas that are used to them. In addition, there will be more droughts, crop failures, melting glaciers, extreme rainfall and floods. Higher temperatures will reduce productivity in developing economies and force more people to leave places that will become more or less uninhabitable, bringing more suffering. The number of deaths from extreme weather is rising.

Climate change may be accelerated by reaching so-called “tipping points.” One key one is Atlantic Meridional Overturning Circulation (AMOC), a system of currents in the Atlantic Ocean that circulates warm water northward and cold water southward. The AMOC helps distribute nutrients for ocean life and keeps some parts of the world warmer than they would otherwise be. Ice core analyses suggest that changes in the AMOC flow have been linked to abrupt climate changes in the past, and it has been observed to weaken over the past century. A 2023 study estimates a 95% chance of AMOC collapse between 2025 and 2095, with the most likely date in the 2050s if greenhouse gas emissions continue at their current rate. A collapse of the AMOC could lead to cooling and drying of northern Europe, stronger storms, shorter growing seasons, and summers more prone to drought. Ocean temperatures off the northeastern coast of America would also rise, affecting fisheries, accelerating the melting of the Greenland ice sheet, and leading to rising sea levels. In addition, the intertropical convergence zone could shift southward, causing droughts in Africa and Central America that would affect tens of millions of people.

The UN’s Intergovernmental Panel on Climate Change (IPCC) has said that 2025 is the year by which greenhouse gas emissions must peak if the world is to have a good chance of keeping global temperature increases within the 1.5-2°C limit set by the Paris Agreement. As the largest emitter of greenhouse gases, China, with 30 % of the planet’s total emissions, is key to the global emissions trajectory. Although its emissions rose sharply in 2023 after COVID-19 restrictions were lifted, analyses suggest that they have fallen by 3 % since March 2024, and may have peaked in 2023.

An alternative to reducing emissions is solar geoengineering, another form of environmental modification that would cool the planet by reflecting incoming sunlight back into space. Research suggests that injecting shiny particles into the stratosphere could be a relatively feasible way to slow or halt the rise in temperatures. However, this method also has physical, chemical and biological effects, which go beyond just affecting temperature, altering the hydrological cycle, the chemistry of the upper atmosphere, and even the rate of photosynthesis. Also of concern are its indirect effects on human affairs, such as the possibility that the level of modification will be determined by the country with the greatest interest in it, unless others intervene through diplomacy or force.

Discussing such choices is difficult and there is no obvious place for it. The UN Framework Convention on Climate Change was not designed with solar geoengineering in mind. However, the ENMOD Convention (Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques) could provide an alternative, as its parties have committed to “international economic and scientific cooperation in the conservation, improvement and peaceful use of the environment.” UN Secretary-General António Guterres, who has passionately denounced the growing impacts of climate change, is in a unique position to initiate such a discussion.

In addition to geoengineering, green technologies are also being developed. Grid-connected energy storage is currently the fastest growing energy technology. By 2025, the combination of solar photovoltaic generation and battery storage is expected to be cheaper than the cost of coal-fired electricity in China and new gas-fired power plants in America. China is investing heavily in green innovation, including hydrogen and carbon capture.

Global efforts to combat climate change include reducing emissions and developing new technologies. However, overcoming the widespread impacts of climate change and managing potential tipping points requires comprehensive solutions, international cooperation and bold policy action. JRi