It's rather a strange statement. How does he think they are related? It's a fact that more CO2 increases plant growth, and warmer climes are very helpful in increasing growing seasons and generally improve life for everyone, especially the poor. It's ice ages that are bad.
Well, one of the things that *could* happen with global climate change is actually a long term cooling trend. Now, I know, you might be asking, how in the world does warming up the earth in the short term possibly make it cooler in the long term?
Well, let me give you an example. Towards the end of the last ice age, there were these huge glaciers over much of North America, right? The earth was warming and we were coming to what would under most circumstances have probably been the end to the ice age. However, because it got a bit hotter, those giant glaciers melted en mass, flooding the eastern seaboard of North America with cold water. That cold water brought down temperatures and extended the ice age another 1,000 years or so. Also, incidentally, the water from those glaciers that didn't wind up in the Atlantic Ocean is what formed the Great Lakes, which is kind of a neat fact.
The earth has a lot of delicate wind patterns and patterns of water flow that help heat and cool it (example:
the gulf stream) and a lot of weird stuff like that. You heat the temperature a little bit, and those get disrupted, and lots of different things are possible, not many of them good.
However, let's just assume that earth heats up and doesn't result in something like inadvertently causing the next ice age, but just warms up. Okay, well, the glaciers at the poles will melt (Some huge ones already have) and the coastlines will rise. There are dozens of cities around the world with cities barely above sealevel that could be permanently underwater. It could be like the flooding in New Orleans after Katrina, but happening to dozens of cities around the globe at once and being a permanent or semi-permanent state. Think of the massive amounts of refugees and the blow to the world economy with dozens of Katrinas that can't be rebuilt from.
Also, think about the deserts of the world. Rough places. To the extent that we live in them, it is often because we can transport water from other areas. For example, parts of Arizona are desert, and they can have a lot of people in them, because the water is brought down from the Colorado river. Now, let's imagine because of warming temperatures, that desert grows and grows and grows. Higher demand for that water, but less of it. That can't be good. Look at what the extended drought is doing to California right now, which could be related to global climate change, but, even if it isn't, is an example of how things could unfold in various places in the future. Similarly, a lot of areas where a lot of food is grown could become desert and result in a global food shortage.
Now, people might say, hey, Canada should be great farmland eventually, let's grow our food up there and bring it down. And maybe we can do that eventually, but those things don't just happen. That's a massive restructuring of what happens where and it costs money.
Also, rising temperatures can mean things like year round poison ivy. Instead of dying in the winter annual, the plants may just keep going. A lot of things might. Exotic tropical diseases could spread further northward global to areas where they haven't appeared previously.
Meanwhile, these temperature changes are causing instability in general in the climate overall. Things like hurricanes occur out of season and in regions where they don't typically happen. We get randomly colder winters in some places because winds come down from the north sort of get cut off and shifted over, which is tough on humans, animals, and plants, people do die of the cold sometimes and have sky-high heating bills.
And, I would guess what Pope Francis will point out is that the people who things impacts most are the global poor. You know how there are food and water issues in Africa now? Imagine what will happen as the Sahara and other deserts get bigger and bigger and there is less and less food and water? A lot of people will die. That doesn't even count the probabilities that fewer resources will mean longer more frequent and more intense wars to gain or keep possession of them.
What happens if, say, Baltimore, New York, and Miami flood? The well off refugees can pick up their lives elsewhere. But what happens to the poor people with no appreciable skills who've lost everything? They'll be a lot of crsises at once and we don't have the capacity to deal with them all.
So, the best way to deal with global climate change is to stop it from happening to the maximum extent we can. Some now is happening and more will happen and to an extent that is irreversible. But we can take action to lower CO2 emissions so it doesn't get as bad as it could if we leave CO2 unchecked. Many organizations are trying to focus on limiting climate change to 2 degrees Celsius worldwide, which they say might be kind of manageable, there'd be crises, but nothing like the death of a billion people and a global economic collapse or whatever. If the temps rise like 8 degrees Celsius, though, God only knows (Literally, God only knows. There are so many variables with that it's hard to say what will happen from a mortal perspective, except that it would very likely be the biggest furthest reaching longest lasting disaster we've ever seen).
