Hi! I'm Jonah Bloch-Johnson, a climate scientist researching global warming. You can learn more about my research here, and see how weird the weather currently is in various cities around the world here. Here's a rundown on global warming:
You and I are powered by the food we eat, breaking down carbon-based matter and in the process breathing out carbon dioxide. We've made machines - cars and power plants and factories - that basically do the same thing, but on a much larger scale, releasing many times as much carbon dioxide in the process. We've made so many billions of machines that the carbon dioxide they produce is noticeably building up in the Earth's atmosphere.
The Sun warms up the Earth, and the Earth in turn cools off by radiating energy away to space; this new carbon dioxide is blocking some of that energy, so that it sticks around and warms up the surface of the planet instead. Even though the temperature on a given day can flicker around like the flames of a fire, unexpectedly getting colder or warmer, this additional energy is like an extra log added to the fire, a persistant additional source that makes the fire warmer on average.
This extra warmth is melting ice sheets, the Arctic ice cap, sea ice, glaciers, and snow; it is bringing more intense heat waves and hurricanes; it is making the sea level rise, changing the Earth's coastlines and bringing worse storm surges; it is shifting the circulation of the atmosphere and ocean and the water cycle, bringing floods to some regions, droughts to others; it is changing the onset and length of the seasons. Also, the carbon dioxide itself is making the ocean more acidic. These changes are altering the conditions that pretty much every living thing on this planet exists in, affecting the web of life in ways that we're still just discovering.
Although we've already altered the climate, we are projected to alter it far more in the coming century and still more beyond, especially as more humans get the benefit of access to these machines that were used by relatively few in the past. Luckily, we have room to be more careful with how we use these machines now, and ways to use them less; and we have new machines that can get energy from other means, like from the wind and the sun, and machines that can store energy; and we have ways of communicating and cooperating as humans, to do whatever we want.
So... what will we do?