What causes the seasons to change?
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Causes of Seasonal Changes: An Overview
Earth's Axial Tilt and Orbital Dynamics
The primary cause of the changing seasons is the axial tilt of the Earth in relation to its orbital plane around the Sun. This tilt, approximately 23.5 degrees, means that different parts of the Earth receive varying amounts of sunlight throughout the year. When the Northern Hemisphere is tilted towards the Sun, it experiences summer, while the Southern Hemisphere, tilted away, experiences winter, and vice versa9. This fundamental understanding is often misunderstood, with many people incorrectly attributing seasonal changes to the Earth's varying distance from the Sun3 9.
Impact of Global Warming on Seasonal Lengths
Recent studies have shown that global warming is significantly altering the lengths and characteristics of the seasons. In the Northern Hemisphere midlatitudes, summer has been lengthening while winter has been shortening. This shift is primarily due to changes in the onset and withdrawal of these seasons, driven by greenhouse warming1. By 2100, under a business-as-usual scenario, summer could last nearly half a year, while winter might be reduced to less than two months1.
Changes in the Growing Season
The growing season, defined by the period during which conditions are suitable for plant growth, has also been affected by global warming. Over the past few decades, the growing season has lengthened by approximately 10-20 days, with an earlier onset being the most prominent change. This extension is linked to rising global temperatures and has significant implications for plant and animal ecosystems, as well as carbon storage and vegetation cover2.
Human Influence on Seasonal Temperature Cycles
Human activities have been identified as a significant factor in altering the seasonal cycle of tropospheric temperatures. Satellite data and climate models have shown that human-caused changes, such as stratospheric ozone depletion and particulate pollution, have led to increased warming in the summer hemisphere and changes in the amplitude of the annual temperature cycle. These changes are more pronounced in the mid-latitudes of the Northern Hemisphere4.
Regional Variations in Seasonal Changes
The impact of global warming on seasonal lengths varies by region. For instance, in the drylands of the Northern Hemisphere mid-latitudes, summer has increased by 0.51 days per year, while spring and autumn have shortened by 0.14 days per year each. These changes are more pronounced in drylands compared to humid lands, with external forcing playing a significant role in these variations5.
Phenological Changes and Ecosystem Impacts
Phenological studies, which examine the timing of natural events, have documented shifts in the timing of seasons, particularly an advance in spring. This shift is linked to increased temperatures and has been observed across various species and locations. The delay in autumn, although less well-documented, suggests that winter is being compressed from both ends, leading to a longer growing season7.
Conclusion
The changing seasons are primarily driven by the Earth's axial tilt and its orbit around the Sun. However, human-induced global warming is significantly altering the lengths and characteristics of the seasons, with profound implications for ecosystems, agriculture, and climate patterns. Understanding these changes is crucial for adapting to and mitigating the impacts of climate change on our planet.
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Most relevant research papers on this topic
Changing Lengths of the Four Seasons by Global Warming
Global warming is projected to lengthen summer by nearly half a year and shorten winter by less than 2 months by 2100, causing disrupted agriculture seasons and increased risks to humanity.
Highly CitedGrowing season changes in the last century
A 10-20 day extension in the growing season has been observed in recent decades, likely due to global warming, potentially impacting plant and animal ecosystems and climate change.
Literature ReviewHighly CitedExploring the reasons for the seasons using Google Earth, 3D models, and plots
Using Google Earth to explore seasonal change helps students better understand the range of factors contributing to climate change and improve their understanding of climate change.
Human influence on the seasonal cycle of tropospheric temperature
Human activity is causing changes in the seasonal cycle of tropospheric temperature, with mid-latitude warming in the summer hemisphere due to continental drying.
Highly CitedChanges in lengths of the four seasons over the drylands in the Northern Hemisphere mid-latitudes
Drylands in the Northern Hemisphere mid-latitudes experienced enhanced changes in spring, summer, and autumn lengths due to global warming, with external forcing playing a stronger role than internal variability.
Projected Future Seasonal Changes in Tropical Summer Climate
Seasonal changes in tropical summer climate, driven by changes in trade winds and Hadley circulation, are projected to increase summer sea surface temperature and decrease winter sea surface temperature, affecting deep convection and precipitation.
Highly CitedObserved changes in seasons: an overview
Climate change is leading to a delay in autumn, causing winter to be squeezed at both ends, increasing the growing season and affecting various species.
Highly CitedQuantitative experiments to explain the change of seasons
This module effectively teaches students about the causes of seasons by using photovoltaic panels to measure sunray flow and introduce basic features of Earth's climate.
Web Resources for the Seasons
The seasons are caused by the Earth's axial tilt in relation to the orbital plane of the Sun and Earth, not the Earth-Sun distance.
Contrasting effects of climate change on seasonal survival of a hibernating mammal
Climate change is likely to positively impact summer survival of yellow-bellied marmots but negatively impact winter survival, highlighting the need for seasonal demographic responses to accurately forecast impacts on animal population dynamics.
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