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Note: The answer grid will include every letter of the alphabet.
BY EMILY COX AND HENRY RATHvON

Combating climate change—it’s not optional. It’s essential at EPA. We will move with a sense of urgency because we know what’s at stake.

—US Environmental Protection Agency (EPA) Administrator Michael Regan, announcing the resumption of the agency’s focus on climate change (March 17). Last month, the EPA updated its Climate Change Indicators website with data from a delayed 2017 report, which states for the first time in the agency’s history that humans are, at least in part, driving climate change.

It is thinkable that the investigation of the behaviour of migratory birds and carrier pigeons may some day lead to the understanding of some physical process which is not yet known.

—Albert Einstein, in a recently rediscovered letter dated October 18, 1949, to radar researcher/actor Glyn Davys. The letter was published in full on May 13.
ACROSS

1. Calcaneal outgrowths
4. Avoided extinction?
8. Last period of the Paleozoic
9. Site of paludal events
10. Output of Karangetang
11. German astronomer Kepler
13. Conception of Mendeleev (2 wds.)
15. Figure ultimately associated with NaCl (2 wds.)
17. Female gamete
20. Sticky-footed lizard
21. Like sides of a scalene triangle
22. Hybridized
23. Predators in black and white

DOWN

1. Component of a calyx
2. Where salmon go to spawn
3. Tibia’s setting
4. Liquid in which a fetus is cushioned (2 wds.)
5. Aggressive predatory foragers (2 wds.)
6. City with a carbon-dated shroud
7. Split along a natural line, as seedpods
12. Shrubs often used in hedging
13. Occurring in the open sea
14. Nest of live bodies made by 5-Down
16. Danish astronomer Brahe
18. Undergoes ecdysis
19. What Fibonacci called “zephyrum”

© JONNY HAWKINS