Why has the temperature of Earth been limited to a more narrow range, for 10 thousand years, when it never was before?
Arctic Ocean Effect Snow is what keeps Earth from getting too hot.
130 thousand years ago, 240 thousand years ago, 335 thousand years ago, 420 thousand years ago, water was trapped on land and it did not get into the oceans until much of the ice on Greenland melted. Therefore, it warmed more than now and melted more ice than now and raised the oceans more than now. Then, the Arctic Ocean Effect Snow was much fiercer and lasted longer than anything in the most recent 100 thousand years. That did drop the oceans enough to cut off all water flow in the Arctic. It then took 100 thousand years to melt the ice sheets and get them thin enough to start to retreat. This melting ice did keep earth cold while the ice sheets thinned. Then, in the most recent major warming, Earth warmed while the ice retreated, until Younger Dryas. The huge amount of ice sheet meltwater dumped into the oceans, early in the warming, and then there was enough water in the oceans to enter the Arctic and produce Arctic Effect Snow without melting Greenland. Now, there is always water in the Arctic and we get Arctic Ocean Effect Snow every time Earth gets warm. The water level now is such that it will always snow before we exceed +2C and the snow will always stop before we go below -2C. Most of the time, the Arctic Ocean Effect Snow will start before +1C, as is happening now, and, most of the time, it will stop before we get below -1C.