From a mailing list I'm on -- a list of big, life-threatening environmental issues that humanity should (but will not, as long as politics is a popularity contest a/k/a democracy and consumerism) address:
* Pollution of land, air, sea and flora/fauna;
* Land overuse killing habitats;
* Genetic destruction through lowering populations below safe breeding threshold;
* Fish depletion;
* Agricultural runoff causing microbial/algic blooms;
* Fences and roads limiting range of animal roaming;
* Climate change and ice melting;
* Most of humanity being under 90 IQ points and thus prone to destroying without creating;
* GM plants spreading into wild;
* Heavy metals contamination;
* Plastic waste floating in ocean and choking national forests;
* Concrete surfaces creating runoff and drought.
It's a good place for us to start thinking about what we'd change. Then all we have to do is figure out how to get the 2-5% of the population that is a ruling class in every society and under every system of government, to approve it.