Switch to energy-efficient light bulbs, wash your clothes in cold water, eat less meat, recycle more, and buy an electric car: we are being bombarded with instructions from climate campaigners, environmentalists, and the media about the everyday steps we all must take to tackle climate change. Unfortunately, these appeals trivialize the challenge of global warming, and divert our attention from the huge technological and policy changes that are needed to combat it.

For example, the British nature-documentary presenter and environmental campaigner David Attenborough was once asked what he as an individual would do to fight climate change. He promised to unplug his phone charger when it was not in use.

Attenborough's heart is no doubt in the right place. But even if he consistently unplugs his charger for a year, the resulting reduction in carbon-dioxide emissions will be equivalent to less than one-half of one-thousandth of the average person's annual CO2 emissions in the United Kingdom. Moreover, charging accounts for less than 1% of a phone's energy needs; the other 99% is required to manufacture the handset and operate data centers and cell towers. Almost everywhere, these processes are heavily reliant on fossil fuels.

Attenborough is far from alone in believing that small gestures can have a meaningful impact on the climate. In fact, even much larger-sounding commitments deliver only limited reductions in CO2 emissions. For example, environmental activists emphasize the need to give up eating meat and driving fossil-fuel-powered cars. But, although I am a vegetarian and do not own a car, I believe we need to be honest about what such choices can achieve.

Going vegetarian actually is quite difficult: one large US survey indicates that 84% of people fail, most of them in less than a year. But a systematic peer-reviewed study has shown that even if they succeed, a vegetarian diet reduces individual CO2 emissions by the equivalent of 540 kilograms – or just 4.3% of the emissions of the average inhabitant of a developed country. Furthermore, there is a "rebound effect," as money saved on cheaper vegetarian food is spent on goods and services that cause additional greenhouse-gas emissions. Once we account for this, going entirely vegetarian reduces a person's total emissions by only 2%.