To what extent do humans modify the climate?

Humans modify climate to a considerable extent. Modification can be on a variety of scales. Globally, since the turn of the 19th century human activity is believed to have modified the net global temperature. However, humans are not the only causes of modification to global temperature. Variations in sunspot activity, Milankovitch cycles, oceanic circulations, meteorites and volcanic activity are all responsible for modifying climate. On a smaller scale, such as the urban microclimate, modification is unequivocally due to humans.

Human have modified global climate in recent decades to a large extent. Humans have emitted CO2 which has increased levels that today stand at around 405ppm, above any other period of history where humans have lived on the earth. 97% of climate scientists agree that this rise in CO2 has been the cause of net global temperature increase seen since the turn of the 1900s. The correlation between CO2 and temperature can be seen most clearly depicted on the hockey stick graph.

Though humans have had recent impact globally, they are not the sole cause of modification in climates history. For instance from 1300 and 1870 Europe and North America experienced the little ice age. This was due to low sunspot activity called the Maunder Minimum which indicated less solar output from the sun and therefore cooler temperatures on earth. The little ice age could also have been caused by the North Atlantic Oscillation which was in ‘negative’ mode bringing very cold winters. This illustrates that human modification of climate is not the sole cause of change seen.

Humans impact on climate to a very large degree on both the local and global scale. Though humans have not been the only cause of climate change in earth’s history it does not subtract from the extent to which today humans are modifying the global climate. In terms of urban microclimates, a debate does not exist; humans modify the climate to a great extent.