These are my own thoughts entirely and do not necessarily reflect those of my employer.
I am not equating climate change with Covid-19.
Covid-19 has garnered a lot of support from effective altruists, and I notice a strong social resolve to encourage social distancing, and create norms such as wearing a mask in your profile picture.
Over time it's become clearer that the mortality gradient for Covid-19 is steepest for people who are older, and who have pre-existing health conditions, but this is only an average. The act of mask-wearing, social distancing etc., becomes less about protecting myself and more about an act of goodwill to others. We undertake this act to reduce the probabilities that we might unknowingly spread the dreadful disease to someone who might become very ill or even die from the disease.
Covid-19 spreads throughout populations, through different means including surfaces and through the air. It produces a nebulous harm, an infection in population. At an individual level, a person catches the infection, and may become very ill. So far (July 2020) there have been around 600,000 deaths globally from Covid-19.
It's an interesting comparison with climate change, which is also a global problem but a very different one. Our actions overall as humanity lead to the production of greenhouse gases, which interact with the earth system, trap more of the sun's energy on earth, and lead to heatwaves, flooding, and increases in the frequency and severity of storms. This leads to human impacts such as heat stress, famines, disease, and death. Our actions as an individual contribute to a nebulous harm, which then affects other individuals. The UN estimates that climate change causes 150,000 deaths per year, increasing to 250,000 per year from 2030 onwards.
We produce these greenhouse gases when we travel on an airplane, drive a car, power our lives, buy products from around the world, and even likely partially powering the computer I use.
John Broome estimates that a lifetime's carbon emissions effectively take away half a year of life from someone else in the world, though it may be higher, and possibly higher still if we take into account the small probability of tragedy. And similarly, my decision to hold a party or interact with my friends during a global pandemic creates some fractional, statistical harm spread across society. These seem to me quite similar.
One difference could be that climate change is more likely to harm people outside of my circle of acquaintances - people living along coastlines and in Sub-Saharan Africa, but covid might affect my own older relatives.