No surprises: Earth’s climate has always changed
One trigger is orbital cycles
warming could mean colder winters!
climate changes on shorter timescales too
Climate change is the natural state of the planet. The Earth’s climate has changed dramatically throughout all timescales: the longest geological timescale measured in thousands of millions of years shows frequent dramatic swings between extremely cold ice-house phases and much warmer-than-present greenhouse phases. Over the 4.5 billion years of Earth history there have been five big ice-house epochs where cold conditions have dominated.
BIG cold snap
The most extreme example was around 700-800 million years ago when the Earth was totally covered by ice, the so-called “snowball earth”. Volcanic eruptions probably released the planet from this particular predicament by ejecting vast quantities of CO2 which warmed the atmosphere. Despite these dramatic deep freeze episodes, for 85% of geological time the Earth has been warmer than it is right now and with much higher levels of carbon dioxide. For example, 70 million years ago CO2 was eight times higher than now and shortly before that it was twelve times higher. Only 15% of Earth history has seen cold ice-house conditions. So the last 2 – 3 million years has been much colder than “average” for planet Earth. During this time there have been several fluctuations into and out of cold conditions called glacials that have typically lasted 100,000 years. The interspersing warmer periods are called interglacials and these have usually lasted about 10,000 years. The cold period of the last 2 million years is popularly known as the Ice Age and more technically termed the Pleistocene.
Dinosaurs: mean but warm
The Ice Age itself has been subject to warmer and colder times. The last really cold snap ended about 10,000 years ago. Modern human existence has developed entirely in this warmer interglacial period over the last 10,000 years but technically we are still living in an “Ice Age” period, merely a warm bit of it, called the Holocene interglacial. Until the 1970’s this warm period was expected to be nearing its end, being about 10,000 years since the last glacial ended, and global cooling was the concern in many climate books of the time e.g. Nigel Calder: “The Weather Machine and the Threat of Ice” BBC 1974.
Orbital cycles are one of the possible causes of regular long-term swings in global climate. The orbit of the Earth wobbles and stretches which affects seasons and energy receipt from the sun. These wobbles occur regularly over 100,000 years. Orbital cycles are the “pace-makers” for temperature change and could be argued to trigger change when other factors coincide with it (like location of continents over polar regions, volcanic eruptions, etc).
Pinning one cold Spring on such large scale cycles would be stretching the evidence somewhat: one cold snap certainly doesn’t prove the climate is changing. Nevertheless, when the Earth’s climate decides to change to another phase, the rate of change is often rapid (called step functions). Spot the steep lines in all of the climate charts: these show how temperature change, once underway, can accelerate and “change gear” quite rapidly. It is the RATE of change happening now that seems to show the Earth’s climate is possibly moving towards a new phase and scientific monitoring seems to suggest this. Moving into a new climate phase could herald a time of more frequent extreme weather like the unusually cold Spring 2013. Whilst blaming “climate change” for “changing weather” is arguably a tautology and not especially useful, climate change, regardless of the cause, must surely be another prime suspect in the death of Spring 2013! At least, there is enough uncertainty not set this prime suspect free just yet!