You wait ages for the bus, and then three come along at once. Books are a bit like that, too, although in this case it's only a pair of them, both tackling the question of what to do about all the "climate refugees". (The United Nations' International Organization for Migration estimates that 1.5 billion people may be forced to move in the next thirty years alone.)
First up is Gaia Vince, a British environmental journalist who has interviewed a great many climate scientists. Her book is Nomad Century: How Climate Migration Will Reshape Our World, and she has certainly grasped the key political problem in a rapidly heating world: some people will be hurt a great deal more than others.
It's mainly a question of distance from the equator. Countries in the tropics and the sub-tropics will be experiencing intolerable temperatures, accompanied by monster storms, droughts and floods, well before mid-century, while those in the temperate latitudes will suffer inconvenience and discomfort but far less actual damage.
In particular, they will still have an adequate food supply, while those nearer to the equator will be seeing their agriculture collapse. That's what will start the refugees moving in their millions -- and 70% of the world's population lives in these vulnerable regions. The only places for them to go for safety are to the richer countries farther north or farther south.
The refugees will feel entitled to settle in those privileged countries, too, since the rich, industrialised countries are responsible for the great majority of the greenhouse gas emissions (carbon dioxide, methane, etc) that have caused the warming. It is astoundingly unfair that the culprits get off lightly while the innocent are ruined -- and the innocent know it.
The mass movement of climate refugees from poor, hot countries to rich, temperate ones is the political dynamite that could destroy global cooperation on stopping the emissions and the warming. Everybody who has been paying attention knows that, but Gaia Vince has a suggestion for dealing with it.
What we need, she says, is "a planned and deliberate migration of the kind humanity has never before undertaken", in which several billion refugees from the worst-hit regions are resettled in the richer, cooler parts of the world. After all, most of the latter countries have falling birth rates, and they'll need someone to look after them when they're old.
And then we have James Crawford's new book, The Edge of the Plain: How Borders Make and Break Our World. He sees the same problem of mass migration, and offers an even more radical solution: the abolition of borders. Away with the fusty rules of the Westphalian system, in which each state has absolute sovereignty within fixed frontiers.
Crawford likes anything that undermines or dissolves those rigid borders, like the "nation" of Sapmi that sort of unites the Lapps of Russia, Finland, Sweden and Norway, or the "climate mobility" advocated by Simon Kofe, foreign minister of Tuvalu.
Mr Kofe's tiny island country will be the first to disappear as the sea level rises, but he wants its sovereignty to continue even though all its citizens must live elsewhere. The sovereignty of the countries that give homes to Tuvaluans and refugees from a hundred other countries would also survive, but shared with the many sovereignties of the new arrivals.
Vince and Crawford are sincere and intelligent people taking on a genuinely existential problem: how can we cooperate to make it through the climate crisis when the pain and the blame are so unequally shared?
Vince writes about having to "shed some of our tribal identities and embrace a pan-species identity", but both authors must know that what they are proposing is unrealistic and unlikely.
Bits of that transition are already stirring, but it's hard to believe that it can supplant the traditional loyalties in the next thirty to fifty years, which is the relevant time frame.
There's also a hidden defeatism here. Both authors assume that the heating will be big and long-lasting enough to force the refugees to move. That's effectively writing off a lot of the planet as a human abode at least for a long time, if not forever.
Vince is well aware of all the partial techno-fixes to the climate crisis that are being discussed or investigated. She does not dismiss "geoengineering" out of hand, but she doesn't see its real potential either.
Holding the temperature down artificially, if it can be made to work safely, is a patch designed to win us time to get our emissions down without a disaster, not a permanent solution to the problem.
But the biggest disaster it would forestall is the climate refugee crisis: if the heating stops not far from where it is now, the refugees never start to move.
Gwynne Dyer is an independent journalist whose articles are published in 45 countries. His new book is 'The Shortest History of War'.
