The effects of global warming include its effects on human health. The observed and projected increased frequency and severity of climate related impacts will further exacerbate the effects on human health.

Warming oceans and a changing climate are resulting in extreme weather patterns which have brought about an increase of infectious diseases—both new and re-emerging. These extreme weather patterns are creating extended rainy seasons in some areas, and extended periods of drought in others, as well as introducing new climates to different regions. These extended seasons are creating climates that are able to sustain vectors for longer periods of time, allowing them to multiply rapidly, and also creating climates that are allowing the introduction and survival of new vectors.

In 2016 the United Nations Environment Programme published a report called: “UNEP FRONTIERS 2016 REPORT”. In this report, the second chapter was dedicated to Zoonotic diseases, e.g., diseases that pass from animals to humans. In this chapter was written that deforestation, climate change, and livestock agriculture are among the main causes that increase the risk of such diseases. It was mentioned that every 4 months a new disease is discovered in humans. It was said that outbreaks that already happened led to loss of lives and financial losses of billions dollars and if future diseases will turn into pandemics it will cost trillions of dollars.

Dengue fever used to be considered a tropical disease, but climate change is causing dengue fever to spread. Dengue fever is transmitted by certain types of mosquitoes, which have been spreading further and further north. This is because some of the climate changes that are occurring are increased heat, precipitation and humidity which create prime breeding grounds for mosquitoes.  The hotter and wetter a climate is, the faster the mosquitoes can mature and the faster the disease can develop.

According to the United Nations Environment Programme the Coronavirus disease 2019 is zoonotic, e.g., the virus passed from animals to humans. Such diseases are occurring more frequently in the latest decades, due to a number of factors, so, as for now, 75% of all emerging disease are zoonotic. Large part of the causes are environmental. One of the factors is climate change. Too fast changes in temperature and humidity facilitate the spread of diseases. The United Nations Environment Programme concludes that: “The most fundamental way to protect ourselves from zoonotic diseases is to prevent destruction of nature. Where ecosystems are healthy and biodiverse, they are resilient, adaptable and help to regulate diseases.”

In April 2020 the United Nations Environment Programme published 2 short videos explaining the link between nature destruction (including from climate change), wildlife trade and COVID-19 pandemic and created a section in its site dedicated to the issue.According to the World Bank climate change can increase the risk of an epydemic like the coronavirus by a number of ways including by causing deforestation. Deforestation is responsible for 31% of the zoonotic diseases.

Part of the causes of the COVID-19 pandemic can be environmental, like climate change and deforestation. They can increase migration of animals and connection between them and humans. This can facilitate the transmission of viruses from one animal to another and to humans. Viruses generally learn to coexist with their host and became violent when they pass to another. The increase in humidity can also make the transmission easier, even though there are suggestions that increase in humidity and temperature may decrease the expansion of the pandemic.

Climate change reduces the number of animals in populations, what lead to less genetic diversity. Such condition facilitates the spread of viruses. Scientists already linked a number of zoonotic diseases outbreaks to floods and droughts and their frequency will increase with climate change. Also, others impacts of climate change can make societies less stable – more wars, human migration, less effective medical and sanitation systems increase the risk of epidemics..Increase in temperature can reduce the capability of the human body to fight the virus, while bats will be less impacted.Climate change can cause food insecurity which can make people eat bushmeat, for example bats, that are possibly linked to the outbreak.