Page 11 - Managing Global Warming

Why do we have global warming? 5

1.2 The root cause of global warming

The scientific evidence that global warming is largely due to the rising CO 2 levels in
the atmosphere is overwhelming and, furthermore, that the rising CO 2 concentration is
due to human activities. Every scientific society and every research organization
working in the field of climate change accepts this view. The atmospheric CO 2
concentration has increased from 280ppm (280ppm or 280 molecules per million
molecules) [9] before the industrial revolution, to 413ppm (observed at Mauna Loa
Observatory on April 26, 2017) [10], and it is this increase of almost 50% that has
triggered the present increase in global temperature.
The most compelling evidence that the increase in CO 2 is the most likely cause
of global warming can be seen in the related graphs of CO 2 concentration in the
atmosphere and the global average temperature as functions of time over the past
many decades (see Figs. 1.1 and 1.2). The CO 2 increase is mirrored by an increase
in the relative increase in average global temperatures over the past 60years.
Monthly mean CO 2 concentration
Mauna Loa 1958 – 2017
Seasonal variation
3 2

390 CO 2 fraction in dry air (mmol/mol) Departure from yearly average -1 1 0
CO 2 fraction in dry air (mmol/mol) 360 -3 Jan Apr Month Oct
-2

Jul

330

1960 1980 2000 2020
Year
Data : NOAAP. Tans
Fig. 1.1 The increase of CO 2 concentration over the past 60years.
Data from Dr. Pieter Tans, NOAA/ESRL and Dr. Ralph Keeling, Scripps Institution of
Oceanography. https://en.wikipedia.org/wiki/Keeling_Curve.