Astronomer royal calls for ‘Plan B’ to prevent runaway climate change

Hacking the planet’s climate by launching mirrors into space, triggering algal blooms in the oceans and seeding clouds are among experimental “Plan B” schemes world leaders would have to consider if the rise in carbon emissions cannot be curbed within a couple of decades, according to one of Britain’s most senior scientists.

Geoengineering, though controversial and “an utter political nightmare”, would buy time to develop cleaner sources of energy, the astronomer royal Lord Rees will say in a speech to the annual British Science Festival in Newcastle on Thursday.

Rees, who is a former president of the Royal Society and a cosmologist at the University of Cambridge, will close the festival with a wide-ranging lecture covering everything from astronomy and global health to the place of science in culture.

On climate change, Rees will say he is pessimistic that global carbon dioxide emissions can be reduced to safe levels within the next 20 years, which means that concentrations of the gas in the atmosphere will rise above 500 parts per million by the end of the century. This level could mean average temperature rises of up to 6C, major melting of the ice caps and, potentially, the triggering of tipping points in the Earth’s climate that would accelerate dangerous climate change. The level of CO2 in the atmosphere passed 400ppm in May.

“If the effect is strong, and the world consequently seems on a rapidly warming trajectory into dangerous territory, there may be a pressure for ‘panic measures’,” he will say. “These would have to involve a ‘Plan B’ – being fatalistic about continuing dependence on fossil fuels, but combating its effects by some form of geoengineering.”

Geoengineering involves deliberate planet-scale interventions to counteract global warming. Several techniques have been suggested including placing mirrors in space that reflect sunlight away from the Earth, to fertilising the oceans with iron to encourage the growth of algae that can soak up atmospheric carbon dioxide. Other options include Rees’s preference – to seed clouds in the upper layer of the Earth’s atmosphere to bounce some of the sun’s energy back into space.

The idea of firing particles into the stratosphere to reduce temperature was inspired by natural events. When Mount Pinatubo in the Philippines erupted in 1991, for example, global temperatures dropped by 0.5C the following year due to the dust it released into the atmosphere.

But enacting such plans would not be without problems. “Geoengineering would be an utter political nightmare: not all nations would want to adjust the thermostat the same way,” Rees will say. “There could be unintended side-effects. Regional weather patterns may change. Moreover, the warming would return with a vengeance if the countermeasures were ever discontinued; and other consequences of rising CO2 – especially the deleterious effects of ocean acidification – would be unchecked.”

In 2009, the Royal Society published a report into geoengineering in which it called for experiments in the various techniques to ensure that their effects and limitations are better understood and the technologies are available as a safety net in case global talks to combat climate change fail.

Doug Parr, Greenpeace’s chief scientist, said that Rees was right about the many downsides and unknowns of geo-engineering. “Yet [he] advances it as a last resort, despite the obvious, much safer things we can do now. It shows the recurrent mirage of a silver bullet solution to climate change is often a sign of despair at world leaders’ unwillingness to seriously tackle CO2 emissions. Every new technology in this field comes with issues, and if they become an excuse for more foot-dragging on slashing carbon pollution they will be harming the climate before even research is done.”

However, Rees will insist that considering geoengineering the climate would not be a get-out for reducing carbon emissions. He will say the world also needs to make a commitment to developing clean energy – extracting and storing power from wind, tides, biofuels, solar or nuclear – that matches the ambition of the Manhattan project in the 1940s to develop the first nuclear bomb or Nasa’s Apollo moon landings in the 1960s and 1970s. “It may take 50 years to decarbonise the world’s power generation, but this could be achieved if we start now.”

Looking ahead in his own field of astronomy, Rees will say he is excited by the regular discovery of planets orbiting other stars. In the past decade, space telescopes such as Nasa’s Kepler have pushed the number of planets scientists know about into the thousands, but they predict there are probably many billions in our galaxy alone, and some of them could be twins of Earth. With ever-improving instruments, he will say, scientists who are now at the start of their careers may be able to answer the question of whether or not there is life beyond Earth.

Back on our own planet, Rees will also call for a more brotherly attitude from his fellow scientists to those of faith. Science, he will say, is the one culture that is truly global and should transcend all barriers of nationality and religion. “The scientists who attack mainstream religion, rather than striving for peaceful coexistence with it, damage science, and also weaken the fight against fundamentalism,” he will say. “But that’s a theme for another talk.”