Tomorrow, over 120 world leaders, including Barack Obama and David Cameron, will gather in New York for a UN summit on climate change. The event, called by Secretary General Ban Ki-moon, comes in anticipation of formal negotiations in Paris next year.

In anticipation of this, Sunday saw the largest climate-change protest in world history, with over 2,800 events held in 166 countries. The largest, in New York, was attended by over 300,000 people. Public concern about climate change is palpable, and feelings are getting ever stronger, as more people demand action from world leaders.

This is not just an issue of scale; there has also been a shift in terms of the make-up of campaigns. A climate-change protest like the one on Sunday would once have been the preserve of minority fringe groups, concerned primarily with conservation and the protection of endangered species.

However, as scientists reveal just how damaging climate change is likely to be, campaigners are uniting in response to arguably more pressing, immediate threats to humanity. – most notably, the risks that climate change poses to global public health.

This isn’t to say that the threats to endangered species and habitat should be ignored. However, as pressure groups routinely target their campaigning efforts in that direction, we shouldn’t forget that climate change does not only affect faraway polar bears and scenic glaciers. Human health is also at risk, and that should provide a strong incentive for our world leaders to pledge action.

The view that climate change threatens human health iis not contentious: the medical community is clear about the risks it poses. Prestigious research journals including Science and The Lancet have dedicated entire editions to the topic, with evidence detailing just how severe the impact is likely to be.

The threats to human health are multi-faceted. We’re all aware of the immediate dangers posed by extreme weather events such as hurricanes and flooding. But these events leave in their wake devastating impacts on health that persist long after the news teams and camera crews have left.

Indeed, the World Health Organization responded to Typhoon Haiyan in the Philippines last year by vaccinating thousands of children to guard against the spread of diseases, including polio and measles.

And the threat of infectious disease isn’t just a distant problem for the countries of the Global South – when Hurricane Katrina hit the US, it resulted in a rise in the number of Vibrio bacteria, the organisms capable of causing diseases such as cholera.

It is clear that even the world’s most sophisticated healthcare systems are likely to have trouble resisting the effects of human-made climate change.

Rising global temperatures also threatens health in other ways. Medical experts predict that changes in climate will widen the habitat of insect vectors carrying diseases such as malaria and Dengue fever.

Indeed, research already shows that changing temperatures have contributed to the spread of malaria to new locations over the last two decades. One report estimates that strains of malaria may be re-established in the UK by 2050.

The direct health effects of rising temperatures are also worth considering. This threat is especially apparent in areas where the temperature goes above the international standard for safe work activity. For instance, in Australia, the number of days breaching this threshold is expected to increase from 5 to 39 days per year.

Rising temperatures are also likely to affect areas where heat doesn’t traditionally pose a health risk. It is worth remembering that a 2003 heatwave across Europe claimed over 35,000 lives in France alone – a worrying statistic considering the extent to which global temperatures are predicted to rise over the next century.

Climate change also threatens nutrition, due to its effects on crop yields and fish supplies – without adaptation, it’s predicted that the number of malnourished children under the age of five will rise by 20 million by 2050.

There is, of course, a significant inequity in these effects. The communities likely to suffer most from the consequences of climate change are those that have contributed the least in terms of fossil-fuel consumption.

The medical community is clear about the threat of climate change, and is urging world leaders to take action at the UN summit this week. Among the protestors in London on Sunday were medical professionals, including representatives from the British Medical Association. And they’re not alone.

Researchers from University College London have described climate change as ‘the biggest global-health threat of the 21st century,’ while the World Health Organization has also recognized the issue as a significant healthcare challenge, having held a conference on the topic just last month.

Such universal consensus from the medical community is rare and disturbing. Campaigners should be forthcoming with such evidence rather than focusing campaigns narrowly on conservation issues.

A recent study found that presenting climate change as a public-health issue provoked a stronger emotional response among members of the public who were otherwise disengaged or dismissive. Such evidence suggests that discussing the health consequences of climate change could prompt more urgent action.

At the UN summit this week, world leaders have a choice: pledge bold reforms to deal with climate change now, or wait for the devastating consequences of inaction. Historically, public-health measures have proved the axiom that prevention is better than cure. When it comes to the global health threat of climate change, that is truer than ever.

George Gillett is a freelance journalist and medical student at the University of Oxford. Follow him on Twitter, or visit his blog here.