Conversely, for the past 3 years, I've worked among geologists and, recently, edited a 400-page textbook detailing the history of Texas geology for the past 1.7 billion years.
Our planet itself is said to be 4.5 billion years old:
We're currently officially in an "Ice Age" (within an Ice Age, there are "glacial" and "interglacial" periods; Earth is currently in an interglacial period):
Interglacial optimumAn interglacial optimum, or climatic optimum of an interglacial, is the period within an interglacial that experienced the most 'favourable' climate that occurred during that interglacial, often during the middle part. The climatic optimum of an interglacial follows, and is followed by, phases that are within the same interglacial and that experienced a less favourable climate (but nevertheless a 'better' climate than during the preceding/succeeding glacials). During an interglacial optimum, sea levels rise to their highest values, but not necessarily exactly at the same time as the climatic optimum.
In the present interglacial, the Holocene, the climatic optimum occurred during the Subboreal (5 to 2.5 ka BP, which corresponds to 3000 BC-500 BC) and Atlanticum (9 to 5 ka, which corresponds to roughly 7000 BC-3000 BC). Our current climatic phase following this climatic optimum is still within the same interglacial (the Holocene). This warm period was followed by a gradual decline until about 2,000 years ago, with another warm period until the Little Ice Age (1250-1850).
Alternating with Ice Ages over the past 4.5 billion years are Greenhouse periods:
The Eocene, which occurred between 53 and 49 million years ago, was the Earth's warmest temperature period for 100 million years. However, this "super-greenhouse" soon became an icehouse by the late Eocene. It was believed that the decline of CO2 caused this change, though there are possible positive feedbacks, or added influence that contributes to the cooling.
The best record we have for a transition from an icehouse to a greenhouse period where plant life exists is during the Permian epoch that occurred around 300 million years ago. In 40 million years a major transition took place, causing the Earth to change from a moist, icy planet where rainforests covered the tropics, into a hot, dry, and windy location where little could survive.
Currently, the Earth is in an icehouse climate state. About 34 million years ago, ice sheets began to form in Antarctica; the ice sheets in the Arctic did not start forming until 2 million years ago. Some processes that may have led to our current icehouse may be connected to the development of the Himalayan Mountains and the opening of the Drake Passage between South America and Antarctica. Scientists have been attempting to compare the past transitions between icehouse and greenhouse, and vice versa to understand where our planet is now heading.
Without the human influence on the greenhouse gas concentration, the Earth would be heading toward a glacial period. Predicted changes in orbital forcing suggest that in absence of human-made global warming the next glacial period would begin at least 50,000 years from now (see Milankovitch cycles).
But due to the ongoing anthropogenic greenhouse gas emissions, the Earth is instead heading toward a greenhouse earth period. Permanent ice is actually a rare phenomenon in the history of the Earth, occurring only during the 20% of the time that the planet is under an icehouse effect.
In the 4.5 billion year history of the Earth, there have indeed been vast swings in climate. But said "vast swings" have taken place over millions of years. Earth temperature records have only been kept for the past 167 years. Because the last 10 years or so have been hotter than the average since 1850, people have suddenly surmised "We're killing ourselves!" Perhaps, instead, Earth is just doing what it's always done for the past 4.5 billion years.
RE the current dismay over the potential plight of polar bears:
Polar bears are thought to have diverged from a population of brown bears that became isolated during a period of glaciation in the Pleistocene or from the eastern part of Siberia, (from Kamchatka and the Kolym Peninsula).In other words, polar bears started out as regular ol' brown bears. If they have to return to being regular ol' brown bears, it's not anywhere close to a drama or tragedy.