Reddit user mredding explained it best in this comment where he states:
In the last 650k years, Earth has gone through 7 periods of glacial advance and retreat. The last was 7k years ago, marking the end of the Ice Age.
CO2 was demonstrated to trap heat in the mid 19th century. In the course of the last 650k years, Earth atmospheric CO2 levels has never been above 300ppm, and we know that through mineral deposits, fossils, and arctic ice leaving telltale predictable signs of how much CO2 must have been in the air at the time. Today, CO2 is over 400ppm. Not only have we kept fantastic records pre-industrial revolution, especially the Swedes for centuries, but arctic ice has acted as a more recent history of the last several dozen centuries. CO2 levels has been growing at unprecedented rates and achieving levels higher than we’ve ever known to occur that wasn’t in the wake of planetary disaster and mass extinction. It follows that if CO2 traps heat, and there’s more CO2 in the atmosphere than ever before, it’s going to trap more heat than ever before.
Sea levels are rising. 17cm over the last century. The last decade alone has seen twice the rise of the previous century. So not only are the oceans rising, but the rate of rise is increasing exponentially.
The Earth’s average temperature has increased since 1880, most of that has been in the last 35 years. 15 of the 16 hottest years have been since 2001. We’re in a period of solar decline, where the output of the sun cycles every 11 or so years. Despite the sun putting out less energy, the average continues to rise and in 2015 the Earth’s average was 1C hotter on average than in 1890. That doesn’t sound like much, but if we go some 0.7C hotter, we’ll match the age of the dinosaurs when the whole planet was a tropical jungle. That’s not a good thing.
The ice caps are losing mass. While we’ve seen cycles of recession and growth, you have to consider ice is more than area, it’s also thickness and density. Yes, we’ve seen big sheets of ice form, but A) they didn’t stay, and B) how thick were they? Greenland has lost 60 cubic miles of ice and Antarctica has lost at least 30 cubic miles, both in the last decade. Greenland is not denying global warming, they’re feverishly building ports to poise themselves as one of the most valuable ocean trading hubs in the world as the northern pass is opening, and it’s projected you’ll be able to sail across the north pole, a place you can currently stand, year-round.
Glacier ice is retreating all over the world, in the Alps, Himalayas, Andes, Rockies, Alaska and Africa.
The number of unprecedented intense weather events has been increasing since 1950 in the US. The number of record highs has been increasing, and record lows decreasing.
The ocean absorbs CO2 from the atmosphere. CO2 and water makes carbonic acid, – seltzer water! The oceans are 30% more acidic since the industrial revolution. 93% of The Great Barrier Reef has been bleeched and 22% and rising is dead as a consequence. The ocean currently absorbs 9.3 billion tons of CO2 a year and is currently absorbing an additional 2 billion tons annually. Not because the ocean is suddenly getting better at it, but because there’s more saturation in the atmosphere.
Citations:
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