In order of concern.
Human-Man global warming is going to be far worse than the worst expectations. It has to be dealt with and the cost will be gruesomely expensive. Six degrees average temperature rise means we lose 99% of all life on the planet, and that includes humans.
Oil and other petrochemical sourced of energy are running out very quickly and catastrophically.
Most natural resources, specifically fish stocks, many rare earth minerals and metal ores are running out catastrophically.
Human populations are still increasing too fast. We need to reduce population growth (specifically in various parts of the third world) as soon as possible. Probably we need to start in years rather than decades.
The corporate sector (and big money in general) has become a carnemonic phenomenon on the planet. We need to get rid of it as soon as possible.
Individual human value is set to collapse with the dawn of ubiquitous automated labour. That means that a soon a sizeable percentage (and not long after the vast majority) of humans will not gain access to an income. This will force a rethink of economy in a matter of years.
Politics as we have it now has become completely corrupted in terms of ineffectiveness. We immediately need fact based governance. Politics appears to be mostly (EU) to completely (US) centered on cultivating and protecting privilege.
The average age of people in the developed world has become completely and catastrophically unsustainable, especially since these people have accumulated very high sets of entitlements, in terms of money and in terms of medical care.
Various modes of denying reality – in specific some religions – are quickly becoming a threat to global human survival. Religion will have to become fully reality affirming, or we need to get rid of it.
Weapons technology is quickly becoming more lethal every year. Right now human species can casually eradicate most life on the planet by even a most casual NBC weapons exchange. In years we have other means of creating genocide in addition to the existing ones. The proliferation of NBC weapons more or less implies we can not afford a collapse.
Feeling optimistic yet? You need to be punched in the face. Wake up. Denial is being complicit to existential risk. Being old (I’ll be dead before this becomes a problem..) is no excuse.