IT IS almost impossible accurately to gauge the scale of yesterday’s global protests calling for urgent action to deal with climate change ahead of the UN summit which opens on Monday, but the organisers planned more than 5,000 events in around 150 countries. With millions of people taking to the streets of cities across the world, there can be little doubt that this has become the single biggest grassroots movement, nor any dispute about the strength of feeling, particularly among younger people.

The scientific consensus is overwhelmingly that climate change presents a huge threat and poses unprecedented challenges – encompassing issues such as desertification, coastal erosion, food and energy supplies and the potential for tremendous demographic, economic and ecological disruption. The prevailing view from these experts is also that not nearly enough has been done by governments, corporations and individuals – especially in the developed world – to take action to tackle what amounts to an existential threat.

Yesterday’s public response suggests that their concerns are now shared by many millions and – after decades in which ecological concerns were regarded as a fringe interest, if not the sole preserve of cranks and treehuggers – have become a mainstream movement for concrete policy changes.

Calls for major change in environmental policy, as well as for individual action, such as the campaigns against single-use plastics, may well now be the single biggest international political demand. And, whatever your views on whether children should walk out of schools to take to the streets, the commitment of the protesters requires a response that matches the scale of the threat climate change is said to pose.

It has, of course, already led to massive changes in priorities for many companies and governments, even if the Climate Emergency movement regards them as inadequate. The UK is in fact one of the most committed countries, and has set a target for net-zero emissions by 2050, while the Scottish Government is more ambitious yet, aiming for 2045, and has made significant progress, though it emerged earlier this month that it has failed to meet the most recent target for 2017.

After a huge push towards renewable energy (it was announced yesterday that offshore windfarms have, for the first time, produced the cheapest generation of all sources), this is an indication of the scale of the problem, and it also suggests that, even if climate protesters are correct about the scale and urgency of environmental threats, their preferred target of carbon neutrality by 2030 may be unachievable.

To make progress towards that goal, however, will require not merely a coordinated international shift in policy, a renunciation of fossil fuels (something where Scotland’s rhetoric is at odds with economic realities), and major changes by nations such as the US and China, where the population have been reluctant to alter their behaviour.

It will also require a realism absent from much of the Green movement’s rhetoric: in particular, opposition to nuclear power, an insistence that markets should play no role in carbon reduction, and a failure to acknowledge the huge economic costs and curtailment of growth their measures would impose, particularly on the poorest nations.

A renunciation of plastic straws may be welcome, but it is a tiny gesture. Electric vehicles will not improve matters if they are powered by a grid still dependent on power stations run on fossil fuels. But the vast majority of yesterday’s protesters are not eco-extremists; they are deeply and correctly concerned that the future may be a much more dangerous place. They are right to call for a major shift in attitudes and, for all our sakes, it is imperative that shift comes as soon as possible.