Last Night's Television: Hot planet, BBC1<br />Spooks, BBC1<br />Gossip Girl, ITV2

Of all the harbingers of climate-change doom, the sunfish must surely have the friendliest face. A round-eyed, massive grey disc of a fish, it swims happily around while waggling its fin above the water in such a way that it looks like it's waving. Cute! Except that where once you had to travel to the balmy waters of the Caribbean to see these little fellows, now you can spot them off the coast of Cornwall. Which, while possibly quite good news for the Cornish tourist board, is devastatingly bad news for our planet.

That the Earth is getting hotter, its oceans warmer, sea levels higher and ice caps smaller was the broader subject of Hot Planet, a handy capsule hour last night for those whose knowledge about climate change goes little deeper than a dim awareness of a big meeting in Copenhagen this week. The stark facts were as follows: if global temperatures continue to rise at the current rate, the Earth will be one degree warmer within 10 years, two degrees warmer within 40 years and three degrees before the end of the century. Already, we live in a world of unstoppable wildfires, malnourished polar bears and levels of greenhouse gases so high that our air is almost 1,000 years older and dirtier than it should be. A "two-degree world" would lead, we were told, to New York being hit by devastating hurricanes and Bangladesh disappearing for good beneath the waves, leaving the rest of the globe to soak up some 35 million "climate-change refugees". A three-degree rise would be utterly catastrophic, resulting in tropical storms over Europe, the melting of the permafrost and, with it, the release of its 1,500 billion tonnes of locked-up CO2, a 23ft rise in sea levels and, as one climatologist succinctly put it, "an arctic region where you could play cricket".

All of this was related with a soundtrack of apocalyptic strings and dour professionalism by Professor Iain Stewart, who, if you closed your eyes and inserted a few CO2-related swear words, sounded exactly like Malcolm Tucker from The Thick of It, which only served to enhance the sense of calamity. Fortunately, he had a perky counterpoint in Professor Kathy Sykes, who abseiled down sandstone canyons in Utah and licked the exhaust pipe of a hydrogen-powered car, to prove that its only waste product was water, in her search for possible solutions. These ranged from the intriguing (injecting carbon into porous rock deep inside the earth) to the futuristic (the world's first carbon-neutral city, Masdar in the UAE, which looked like something out of The Jetsons) to the barmy (firing millions of mirrors into orbit to reflect sunlight away from the Earth). Most fascinating was an introduction to the world's first artificial meat, grown in a lab from animal cells to counteract the vast quantities of greenhouse gases produced in rearing livestock. At this stage, the meat – a loose term for this tiny gelatinous blob – still can't be cooked or eaten. Well, of course. "It reminds me of something," said Heston Blumenthal, doubtfully. "Raw liver. Or a baby slug." The chef also described it as the most surreal thing he'd ever seen, food-wise, which from the inventor of parsnip cereal is probably an accolade. It was certainly pretty jaw-dropping stuff, but after an hour of these fantastically inventive schemes came the creeping, hollow-stomached realisation that it would have been a whole lot easier if we hadn't made such a terrible mess of it all in the first place.

Apocalypse of a different kind was on offer in Spooks, in which the UK found itself in the chilly shadow of a (hastily glossed) "economic eclipse" and facing the prospect of bankruptcy by Saturday morning. The only man who could stop it was Ryan Baisley (nicely deranged Ewen Bremner), MI5 asset and rogue employee of the corrupt DeWits bank (former client: Saddam Hussein). Having started fairly slowly, it's safe to say that series eight of the spy drama has now hit its stride. This was a thrilling, if explosively bloody, episode with a chase through Liverpool Street station, Ros (icy Hermione Norris) torturing a banker in a car park and a gunpoint stand-off between MI5 hero Lucas and his CIA baddie girlfriend, Sarah. Spooks has still got it.

I'm not sure that the same can be said for Gossip Girl, which now feels, as Blair Waldorf would say, so last fall. This week among the usual shiny-haired mix of drug-dealing diplomats, extra-marital affairs and threesomes came a much-hyped cameo from Lady Gaga. The flimsy premise was Blair's ambition to become queen bee at Tisch – NYU's performing arts school – by inviting its most eccentric alumna (back then she was just plain old little rich girl Stefani Joanne Angelina Germanotta) to perform. When the pop star finally arrived, she was restricted to a whirling dervish pop video of a performance in the background of the break-up of Dan's dull love triangle. Given La Gaga's weekend triumph on The X Factor, where she appeared as a cyber-bat doing Bollywood dance moves in a giant bath, I expected a little more.