In this case, CO2 is not the immediate cause of ice ages rather, it serves as a feedback to amplify changes initiated by orbital variations. These shifts in the distribution of sun’s energy across the Earth’s surface are not enough to explain the dramatic changes to the climate during ice ages, particularly outside high-latitude regions.Ĭhanges in atmospheric greenhouse gas concentrations – and, in particular, CO2 – play a large role in the development of cold conditions during ice ages and warm conditions during interglacial periods. The northern latitudes matter much more than the southern latitudes – at least over the past few million years – as it contains more land area (which can more easily become ice-covered than the oceans) and because the Antarctic has remained covered in ice. These ice sheets in turn reflect more incoming sunlight back to space, resulting in a “positive feedback” that drives additional regional cooling. When these cycles cause the northern latitudes to get less sun in the summer, it allows ice sheets to begin to expand. None of these cycles substantially changes the total amount of energy reaching the Earth from the sun rather, they mostly act to change the distribution of the sun’s energy across the surface of the Earth. These three cycles overlap in different ways over time given their different periods, which means that ice ages do not always have the same duration.
The most recent ice age occurred between 120,000 and 11,500 years ago, while the current interglacial period – the Holocene – is expected to last for additional tens of thousands of years (and human activity may inadvertently delay the start of the next ice age even further). These ice ages are punctuated by “interglacial” periods where temperatures rise to around current levels. These ice ages are associated with a large drop in global temperatures – 4C or more below today’s levels – with much larger changes over land and in the high latitudes. The Earth has experienced a number of periods over the past million years in which large continental ice sheets have covered much of the northern hemisphere. It also acts as a cautionary tale of how the climate can experience large changes from relatively small outside “forcings”. In this explainer, Carbon Brief explores how the last ice age provides strong evidence of the role CO2 plays as a “control knob” for the Earth’s climate. There is a real risk that, if emissions continue to rise, the world warms more this century than it did between the middle of the last ice age 20,000 years ago and today.
The global average temperature was around 4C cooler during the last ice age than it is today. But changing atmospheric concentrations of CO2 also plays a key role in driving both cooling during the onset of ice ages and warming at their end. These ice ages are triggered and ended by slow changes in the Earth’s orbit.
Methane global ice driver series#
The past million years of the Earth’s history has been characterised by a series of ice ages broken up by relatively short periods of warmer temperatures. Prior to that, the Earth experienced an ice age lasting for tens of thousands of years. The Earth’s climate has been quite stable over the past 11,000 years, playing an important role in the development of human civilisation.
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