Because we live in Como, surrounded on three sides by water, and live only a couple of metres above water level, the matter of climate change is really important to us. I've written a very short synthesis of human existence in the context of climate. I hope you find it interesting.
The Earth is about 5 Billion (five thousand million) years old. For most of that time the planet has been a hot place, certainly devoid of any ice.
During the most recent half of our planet’s existence, however, there have been four ice ages, times when major ice sheets covered at least part of our planet. The earliest well-documented ice age, about 700 million years ago seems to have produced a Snowball Earth in which permanent ice covered the entire globe. The present ice age began 40 million years ago with the growth of an ice sheet in Antarctica. It intensified around 3 million years ago, with the spread of ice sheets in the Northern Hemisphere. Since then, the world has seen cycles of glaciation, with ice sheets advancing and retreating on 40,000- and 100,000-year time scales.
Ice cores drilled a thousand metres into the Antarctic ice at Vostok, the coldest place on Earth, show us a history of Earth’s temperature over this recent time. Note that the plot covers the most recent half a million years only (one ten thousandth of the Earth’s life), and reads in thousands of years Before Present.
For original data see Vostok Ice Core or just click on the plot above to enlarge it.
What you see in this history is a cycle of temperature covering ten degrees, changing on a fairly regular pattern.
We are presently at the end of a long ice age cycle, a time when significant ice sheets exist on the Earth's surface. It is very clear from this plot that the planet is warming, and has been doing so for thirteen thousand years- that's the time of the sharp jump on the left side of the plot.
Since the great ice sheets of the northern hemisphere retreated eleven thousand years ago, almost all of human migration and human history has occurred. As the ice sheets, up to two kilometres thick, melted away, most of the planet became habitable to humans, and we managed to cover the planet with ourselves, rapidly.
We live today over the sands of the Perth Coastal Plain, on dunes formed during the most recent Ice Age, about 100 thousand years ago. During that very brief time the sea level has been both higher and lower, taking the coastline both inland to the hills and out to sea past Rottnest. The evidence includes layers of shells we see when we dig in our gardens, fossil tube worm burrows on cliff tops at the beach and submerged cliffs that we see when snorkelling.
What concerns us now is that our existence in this generally, relatively speaking, green and pleasant world depends upon a particular balance of temperature, rainfall, sea levels and myriad other finely balanced factors. These factors change, and have been in change for the entire history of the Earth.
Are we making this change faster? There are many reports of acceleration in warming, some of which are highly credible. For example, see Glacial Thaw
Some really interesting things are happening now, to do with the science of climate change, the ways that our waste production and management might be influencing that change and matters of management of risk associated with these changes.
Please have your say and add to our understanding by clicking on "Comments" below.
No comments:
Post a Comment