Make up a new global threat on the level of global warming.
A made up threat with large scale effects on the world could be as follows:
A rogue planet passing through our solar system has caused earth to slowly spiral away from the sun.

To explain why this is on the same level as global warming, consider the following:
 - The slow movement away from the sun will gradually cause the world to cool down, as the sun's rays grow weaker. This cooling effect will drastically affect global food production, and eventually cause crop failures as the climate rapidly drifts from normal. This will, expectedly, cause massive human suffering in various forms such as famines, social unrest and falling goods supplies.
 - This threat mirrors global warming in its predictability before the turning point: A rogue planet approaching earth would have been noticed years or even decades in advance, allowing the possibility for plans to be enacted to avoid pr otherwise defuse the threat.
 - The threat will not equally impact all of the world, like global warming: Food shortages will affect countries which import it more that exporters. Weakening sunlight will cause regions dependent on solar to suffer energy shortages, while other regions which use non-solar energy will be able to avoid the shortage. Goods like cotton, bioplastics, and other plant based substances are usually very regional in their production, and this will affect trade and the well being of those farming the resource.
Can you provide a brief summary of a story about the discovery of this looming danger and humanity's desperate attempts to stop it?
A faint new point of light in the sky observed by astronomers was too far out be a comet; it was much bigger. As a rogue planet passed by our solar system it was never more than a faint speck of light against the dark night to the naked eye. But, that was enough. How could something that appeared so tiny - something so far away - harm us? Astronomers sounded the alarm. For the most part they were ignored. But what could anyone do anyway? With the mass of Jupiter the passing planet was too big to divert. The international space station was upgraded to support long term habitation for the lucky - or unlucky - few hundred who would attempt to sustain humanity in space for as long as they were able. As the interloper left our solar system its gravitational pull dragged Earth ever so slightly away from the sun. As Earth started to spiral away from the sun, the effects were small at first; a drop in global temperature and some unusually cold weather. As Earths orbit became wider and wider, the fate of life on our emerald world was sealed, destined to be entombed in ice and a mix of solid Nitrogen and Oxygen; all that was to remain of our atmosphere. In their last years, the remnants of humanity created monuments recording our history, hoping that one day, billions of years into the future, our planet would be discovered by another sentient species and they would learn of our story. Our icy tomb drifted into the void.