Global temperature history
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Global Temperature History: An Overview
Holocene Temperature Trends
Early Holocene Warmth and Mid-Holocene Cooling
The Holocene epoch, spanning the last 11,300 years, has seen significant temperature fluctuations. Early Holocene temperatures were relatively warm, followed by a cooling trend of approximately 0.7°C through the middle to late Holocene. This cooling culminated in the Little Ice Age around 200 years ago, characterized by the coldest temperatures of the Holocene .
Recent Warming and Current Temperatures
Since the end of the Little Ice Age, global temperatures have risen steadily. Current global average surface air temperatures are warmer than those during 90% of the Holocene, although they have not yet exceeded peak interglacial values. Projections for 2100 suggest that temperatures will surpass the full distribution of Holocene temperatures under all plausible greenhouse gas emission scenarios .
Common Era Temperature Patterns
Lack of Coherent Preindustrial Warm and Cold Periods
Over the past 2,000 years, known as the Common Era, there is no evidence for globally coherent warm and cold periods before the industrial era. The Little Ice Age, for instance, experienced its coldest temperatures at different times in various regions. In contrast, the 20th century has seen unprecedented global warming, both in terms of absolute temperatures and spatial consistency .
20th Century Warming
The 20th century stands out as the warmest period of the past two millennia for more than 98% of the globe. This period of warming is unparalleled in its spatial coherence, highlighting the significant impact of anthropogenic factors on global temperatures .
Long-Term Temperature Evolution
Past Two Million Years
Over the past two million years, global temperatures have shown a gradual cooling trend until about 1.2 million years ago, after which the cooling stalled. This period includes the mid-Pleistocene transition, characterized by a shift to quasi-100,000-year glacial cycles. The close coupling of global temperatures and atmospheric greenhouse gas concentrations across glacial cycles suggests a high sensitivity of the Earth's climate system to greenhouse gas levels .
Phanerozoic Eon (Last 540 Million Years)
The Phanerozoic eon, covering the last 540 million years, has seen significant temperature changes influenced by geological processes. The Earth's climate has oscillated between warm and cool periods, driven by factors such as volcanic eruptions and bolide impacts. These long-term temperature patterns provide insights into the fundamental causes of climate change on geological timescales .
Recent Temperature Records
1979-2010 Temperature Trends
From 1979 to 2010, global temperatures have shown consistent warming trends across various datasets. Adjusted data, accounting for factors like El Niño, volcanic aerosols, and solar variability, reveal a clear global warming signal. The two hottest years in this period were 2009 and 2010 .
Surface Air Temperature Changes Over 150 Years
Over the past 150 years, global surface air temperatures have risen significantly. The 20th century saw two major warming periods: 1925-1944 and 1978-1997. Recent decades have experienced greater increases in night minimum temperatures compared to day maximum temperatures, leading to a decrease in the diurnal temperature range .
Conclusion
The history of global temperatures reveals a complex interplay of natural and anthropogenic factors. From the early Holocene warmth and mid-Holocene cooling to the unprecedented warming of the 20th century, understanding these patterns is crucial for predicting future climate changes. The evidence underscores the significant impact of human activities on global temperatures, particularly in recent decades.
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