Earth is rapidly becoming uninhabitable by humans and many other species. Lately, and most critically for humans in near future, the climate is changing for the worst. Scientists interested in the truth are in the process of determining its exact trajectory based on what they continue to learn about the complex variables and systems that affect it, but they have no significant doubt about the general direction and the major reason why it is headed there: the atmosphere is trapping more and more heat due to humans releasing large amounts of greenhouse gases into the atmosphere. We are also influencing the climate in other ways, directly and indirectly; some effects are positive (such as pollution causing more sunlight to be reflected into space, having a cooling effect) and some are negative (darkening ice, causing it to melt and reflect less sunlight into space). The net effect is negative from the viewpoint of our ability to live here, which includes: contributing to greater uncertainty in availability of food and fresh water; increasing the amount and severity of floods and storms; and increasing temperatures so that more of us die from heat exhaustion.
The most obvious response to this existential threat is to stop doing what we're doing to cause it. This means abandoning our use of fossil fuels, which is the main source of greenhouse gases. It also means stopping our wholesale pillaging and destruction of other species and their habitats, species who have evolved to keep the planet habitable for themselves and others. On a deeper level, it leads to rewriting the definition of civilization to prioritize coexistence over exploitation, setting limits on our pursuit of resource-intensive happiness so that members of all species, including our own, can contribute constructively to maintaining a healthy, shared home.
Another response to the threat is to try dealing with the direct impacts, expanding our access to resources even more, so we can continue growing both our numbers and the creation of environments that maximize our happiness. Included in this response are various forms of geo-engineering, such as the development of new foods using genetically modified organisms (GMOs) that can live in the inhospitable environments we've created; removing excess greenhouse gases from the atmosphere; and blocking sunlight to manage temperatures at Earth's surface. Because this response doesn't account for the complexity of the systems and processes it affects, and proliferates the very approaches that created the current threat in the first place, it has the potential to itself create many more threats.
We could, alternatively, try to escape the threat. This might involve anything from building huge, underground habitats, to moving some people to another world where they have a better chance of survival. Neither option is practical for a significant fraction of our population, even if they could be exercised at all (or safely) in the time we have left before the threat becomes overwhelming, which could be anywhere from one to eight decades.
A fourth response is to deny that the threat even exists. This response includes dealing with the threat's consequences without knowledge or preparation, except to the extent that those consequences resemble otherwise acknowledged conditions. It also involves opposing any use of resources to support the other responses. Such a response has the effect of increasing personal jeopardy and the jeopardy of others who can be influenced to respond the same way.
If, as some scientists fear, we have activated multiple natural processes that are accelerating climate change, making it already too late to take any action that avoids the total extinction of our species, several other options present themselves. We could resign ourselves to that fate, like someone with a terminal disease, and try to have as much quality of life as possible until the end. For some, this will be too much to bear, and they could consider suicide before conditions become unbearable.
Based on population collapses of the past, the "unbearable" conditions following lack of success in reducing the threat (and avoiding worse ones) would be accompanied by increasingly violent competition for the remaining resources needed for survival. This fate is a certainty if it's either too late, or enough of us postpone significant remedial action until it becomes too late (such as if we are in denial, or if we believe failure is inevitable when it is not).
To take remedial action, it is psychologically necessary to have some hope that it will be successful. Among a growing number of people who are convinced that our extinction is practically inevitable, this is called "hopium," a drug that just makes us feel good. I suggest that the alternative be referred to as "mopium," because acceptance of the ultimate failure can lead to listlessness, depression, and in some cases suicide. Treating the symptoms of moping toward oblivion may deal with the feelings, but it also contributes toward making that fate more certain by inhibiting action to deal with the cause, both directly and indirectly (by criticizing others who threaten the failure worldview by believing action may succeed).
Advocates of remedial action have focused mostly on reducing what I call "dopium": intentional ignorance characterized by belief that the threat isn't real, and that remedial action itself represents a threat. Its causes are many, including misinformation campaigns intended to maintain the status quo, operated by a relative few who stand to lose substantial economic and social power that the status quo affords them, and stand to gain the most (in the short term, anyway) by panicked responses to future disasters. We need to instead focus on reducing both dopium and mopium if we are to marshal the human resources necessary to deal with the imminent threat at hand.