Independent data shows that the Earth’s average surface temperature has warmed by about 1.1°C since the Industrial Revolution in 1850. This global warming is becoming a clear sign that human emissions of greenhouse gasses are changing the planet’s climate.
Besides from human activities affecting the climate, large amounts of energy are transferred naturally within the climate system, particularly between the atmosphere and the oceans. This affects global temperature by creating temporary warmer or colder periods.
The reason for this can be explained by increasing atmospheric CO2 concentrations. It has increased from 280 parts per million in 1850, to more than 400 parts per million today. This shows that human emissions of greenhouse gasses are responsible for increasing global temperatures because natural climate processes cannot cause fast increasing temperatures.
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To understand the relation of human activities to natural variations in the climate system, scientists use complex computer simulations. This model calculates temperature, wind, humidity and other meteorological parameters that are part of the natural climate system. Models will only show temperature changes consistent with warming from emissions of human activities. This shows that greenhouse gasses emitted through human activities have been the main cause of global warming since 1850.
Natural factors also influence the climate, like warm water rises from below the ocean and pours heat into the atmosphere or El Niño. Radiation from the sun also has a strong potential to affect the temperature of the atmosphere. Scientists have measured solar radiation using satellites, and shown that over the last 10,000 years, the sun’s energy has varied.
Climate sensitivity is the way global temperatures respond to increasing CO2 in the atmosphere. Scientists currently estimate that the climate warms by about between 1.5°C and 4.5°C every time the concentration of CO2 in the atmosphere doubles.
Source: Imperial College
