According to the Lancet Commission on Health and Climate Change, an interdisciplinary group formed by UK-based medical journal The Lancet, climate change has a huge impact on human health. The commission was formed to investigate exactly that fact, and they have recently released a study, the most comprehensive ever done, on the impact climate change has on human health.
In short, the impact is quite negative. The commission argues that climate change is undoing the last half a century of amazing medical advances, for a number of reasons. Most obvious would be carbon emissions, which pump far more CO2 into the atmosphere than the Earth can currently handle. This can lead to all kinds of health problems, not to mention environmental issues. In fact, they suggest that fossil fuels, especially coal, are the worst health factor in the world, but that we could do a lot of good by cutting those things out immediately, or at least as soon as possible.
Another, more subtle threat, is human migration. Migration has always been a part of the human experience, but it brings with it certain problems, especially when large groups of people move quickly to a new place. Diseases spread faster, and resources become scarcer, impacting everyone. As humans render regions unlivable, people will have no choice but to more somewhere else.
Although the various experts who form the commission have a lot of bad news, there is a silver lining. They hope that, by framing climate change as a human health issue, people will be more likely to respond and actually do something about it. Doctors managed to put big tobacco in its place, for example, so maybe they can do the same to big oil and big coal. As they pointed out, a doctor with a sick patient would do something about that patient, not just talk about it once a year, which is pretty much all we’re doing about climate change so far.