The Pope holds a great deal of moral authority. Scientists not so much.
I've read Laudate Si'. It's not really about the science, or arguing that AGW is true, or that biodiversity is being lost, or that pollution is killing people. It takes these things for granted but it does not marshall evidence per se.
It's main point is that AGW, true or not, is evil and must be stopped, and it ties this into social teaching by associating the consumer culture of rich countries with the exploitation and immiseration of small, poor ones; mankind's moral obligation to protect the Earth, and it asserts baldly things like "man has no right" to push a species, any species, even the smallest plankton, to extinction (Francis actually mentions plankton).
I don't hear scientists talk like this, and that's fine, it's probably not their place. But evidence isn't enough to actually move people to action, you do actually have talk about right and wrong, and why this thing is wrong and must be stopped. And Francis specifically argues against the idea that technology will one day solve this problem for us, to him the problem with the planet is 100% between people's ears, it has to do with the way modern people see the world as a resource to be exploited. Don't ask me to defend this, I think he's a little too pessimistic here, but it just continues the idea that his argument isn't about science, or technology, or even the material world, to him it's fundamentally spiritual.
And he has a point; why should we care about climate change if the Earth if it's just a ball of dirt and we can just fly a rocket to another one? Science can tell us what the planet is and where it's going, but it can't tell us if that's a good thing or not. So does Krauss think scientists should hold more moral authority than a Pope? Is that the paradox here? Should scientists teach us right and wrong?