informally, a global issue describes any social, economic, political or environmental problem that affects the global community, possibly in a catastrophic way.
Solution to global issues requires cooperation among nations.
In their book Global Issues, Hite and Seitz emphasize that global issues are qualitatively different from international affairs and that the former arise from growing international interdependencies which makes the issues themselves interdependent.
The UN has listed issues that it deems to be the most pressing as of 2015:
United Nations High Commissioner for Refugees (UNHCR)
Theories like the world-system theory and the Gaia hypothesis focus on the inter dependency aspect of environmental and economic issues. Among the most evident environmental problems are overpopulation, resource depletion, pollution, water pollution, waste and waste disposal, ocean acidification, acid rain, ozone layer depletion, global warming/climate change, loss of biodiversity and habitat loss, deforestation, and urban sprawl.