Mitigate Global Catastophes

There are several known existential dangers to human life. This list is meant to explain —

Our current protections against these dangers
The main stressors and triggers
Mitigations we can do as individuals and societies

It's also meant to encourage broad support for these mitigation efforts.

The Known Dangers

Pandemic — This includes bioengineered organisms and naturally-occuring organisms that wipe out large portions or the entirety of a population.
Cosmic Threats — This includes impact with a large asteroid, a gamma-ray burst, powerful solar flares or superstorms, and passage of our solar system through a dark nebula or a cloud of cosmic dust.
Volcanism — This includes a geological event such as the eruption of a supervolcano, massive food basalt, volcanism, or the eruption of a supervolcano.
Climate Change — This includes human-caused global warming, natural climate change, and climate change induced by a threat such as an asteroid impact or supervolcano.
Agricultural Crisis — This refers to a sudden reduction in the available food supply, leading to mass starvation. One project to mitigate this risk is the Svalbard Global Seed Vault. Other efforts could include increasing local and personal long-term food storage, and distributed heterogeneous agriculture and reduction of monocrops. This risk is reduced with population reduction. It's also reduced with agriculture technology that improves crop yields, caloric and nutrient content, and storage and transport time.
Warfare & Weapons of Mass Destruction — This includes world war, nuclear war, and massive use of chemical and biological weapons. The damage could be directly ending many lives and destroying large amouts of resources used to sustain the population. This could be triggered by competition for a critical agriculture or mineral resource, a global economic meltdown, or by imperialism of a powerful country.
Instrastructure Breakdown — This includes widespread breakdown of critical infrastructure like clean water supply, electricity, or transportation. It could be triggered by cyberattack or a deficiency in a critical enabling resource.
Artificial Intelligence — ...

Beyond specific mitigations for each danger, there are some broad possibilities that mitigate several dangerous at once.

Governance — That enforces limits on the factors that increase these risks, such as population growth and resources consumption. Governance can also regulate dangerous technology and require small-scale introductions of risky changes.
Culture & Education — Support for mitigation efforts will increase if the social norm is concern for these dangers, and if we are educated about the risks and mitigation possibilities.
Space Colonization