The climate! Right now a bunch of old people worried about the economy and their health care - every youngster on earth is soon eligible to vote. None have a chance at a good economy, none have a chance at health, none have a chance at world peace, none have a chance at having their own families - its the climate. That is the biggest issue.
Rising waters and coastal hurricanes and tsunamis will redraw the map. Wars will ensue as billions seek refuge elsewhere. Economic devastation will progress as war takes its toll and industry has to learn to function without fuels, their alternative sources as of yet undeveloped or unavailable.
Naval choke points will become an issue, the shortest way from the Atlantic to the Pacific will become through the northwest passage, (no longer a seasonal route), while dodging oil rigs erected in those waters by Russia and America.
Inland floods and droughts will wreak havoc on agriculture causing shortages of foods for export exacerbating the problem on dependent nations., redrawing which nations are importers and exporters.
Right wing military dictatorships now forming in Brazil, The US, and other nations are amassing power will make their moves on a global scale as opportunities in the form of resource rich nations weakened by disaster present themselves.
No other political issue can be duly considered without considering the impact of climate change. This is the world left by the duopoly to today’s teenagers, soon to be of voting age