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CONVERSATIONS 1: Climate Change 

 

Climate Change: the Science 
 

Robert Watson  
 
There is no doubt that the earth’s climate is changing on all scales, from 
local to global—in large measure due to human activities, primarily the 
combustion of fossil fuels and large-scale deforestation. Climate change 
undermines economic growth, poverty alleviation, and the livelihoods of 
the poor; and threatens socio-economic sectors (food and water security, 
for example), ecological systems, human health, and personal and national 
security. 

The major indirect drivers of climate change are primarily demographic, 
economic, socio-political, technological, cultural, and religious. These 
drivers are clearly changing; for example, the world’s population is 
projected to increase from just over 7 billion people today to 9–10 billion 
people by 2050. There will likely be an accompanying increase in the global 
economy by a factor of three or four. Increasingly, developing countries will 
drive global economic growth. These projected increases in population and 
the economy are certain to result in increased demand for energy. 

There is no doubt that the composition of the atmosphere and the earth’s 
climate has changed since the industrial revolution; and it is inevitable that 
these changes will continue—regionally and globally. The atmospheric 
concentrations of carbon dioxide, methane, and nitrous oxide are higher 
than at any time in the past 800,000 years; and the atmospheric 
concentration of carbon dioxide, the major anthropogenic greenhouse gas 
(GHG), recently exceeded 400 parts per million by volume (ppmv). Each of 
the past three decades has been warmer than the previous decade. The 
global mean surface temperature has already increased by about 1 °C 

                                                        
 Strategic Director of the Tyndall Centre, University of East Anglia, Norwich Research 
Park, Norwich NR4 7TJ, UK; rtwatson1@gmail.com 

Copyright © Watson 2018. Released under Creative Commons Attribution-NonCommercial 
4.0 International licence (CC BY-NC 4.0) by the author.  

Published by Indian Society for Ecological Economics (INSEE), c/o Institute of Economic 
Growth, University Enclave, North Campus, Delhi 110007.  

ISSN: 2581-6152 (print); 2581-6101 (web). 

DOI: https://doi.org/10.37773/ees.v1i1.16  

https://doi.org/10.37773/ees.v1i1.16


Ecology, Economy and Society–the INSEE Journal [70] 

relative to pre-industrial levels. The low emissions scenario projects that the 
global mean surface temperature will increase by 0.3–1.7 °C by 2100; the 
high emissions scenario projects that it will increase by 2.6–4.8 °C. The 
greatest increases are projected for land areas in the high northern latitudes. 

Changes in temperature and precipitation are causing, and will continue to 
cause, other environmental changes. Such changes include rising sea levels; 
retreating mountain glaciers; melting of the Greenland and Antarctic ice 
sheets; shrinking Arctic Sea ice; increasing frequency of extreme weather 
events, such as heat waves, floods, and droughts; and intensification of 
cyclonic events, such as hurricanes in the Atlantic. The sea level has risen by 
about 0.2 metres since 1900, and is projected to increase by an additional 
0.3–0.6 metres by 2100 in the low emissions scenario or by 0.5–1.0 metre in 
the high emissions scenario. Annual Arctic sea ice extent has decreased by 
3.5–4.1 per cent per decade during the past three decades, and summer 
Arctic sea ice minimum extent has decreased per decade by 9.4–13.6 per 
cent, with further reductions projected in September of 43–94 per cent by 
2100. The rate of ice loss from the Antarctic ice sheet between 2002 and 
2011 increased significantly compared to the rate between 1992 and 2001. 

Enhanced atmospheric concentrations of carbon dioxide cause, and will 
continue to cause, ocean acidification, which poses risks to fish, especially 
shell fish and marine ecosystems, especially coral reefs. 

The Working Group I of the Intergovernmental Panel on Climate Change 
(IPCC) in 2013 concluded that the human influence on the climate system 
is clear, and that it is extremely likely that human activities have been the 
cause of more than 50 per cent of the observed warming (0.6–0.7 °C) since 
the mid-twentieth century. The IPCC considers it likely that anthropogenic 
activities have influenced the global water cycle; such influence includes 
global-scale changes in precipitation over land and intensification of heavy 
precipitation over land regions with sufficient data. 

Every government in the world recognized the danger associated with 
human-induced climate change and signed the Paris Agreement in 2016, 
though the US has since withdrawn. Under the agreement, governments 
pledged to hold the increase in global average temperature well below 2 °C 
(above preindustrial levels), and to pursue efforts to limit the temperature 
increase to 1.5 °C above pre-industrial levels. To realize these targets, a 
rapid transition to a low-carbon economy is required, which involves 
unprecedented global cooperation and a dramatic transformation in energy 
systems. 

Governments acknowledged that achieving the Paris Agreement goals 
requires balancing anthropogenic emissions by sources and removals by 



[71] Robert Watson 

sinks (the oceans and terrestrial biosphere) in the second half of the 21st 
century. In reality, most models require negative emissions beyond 2050 to 
achieve these targets. As part of the Paris Agreement, 162 voluntary non-
binding pledges were submitted to the United Nations Framework 
Convention on Climate Change (UNFCCC); these were from 189 countries 
and accounted for about 98 per cent of global GHG emissions. 

While these pledges demonstrate a real increase in commitment to reduce 
GHG emissions, they are far from sufficient to put the world on a pathway 
to meet the 2 °C goal—let alone the aspirational goal of 1.5 °C. Without the 
Paris Agreement, global emissions of carbon dioxide-equivalent are 
projected to increase from the current level of 54 gigatons to 65 gigatons by 
2030, but these will have to be reduced to about 42 gigatons for the global 
average temperature to stay below 2 °C. However, even if all pledges were 
fully implemented, global emissions would remain at about their current 
level, and result in an increase in global mean temperature of between 3oC 
and 4oC above preindustrial levels. Therefore, without significantly stronger 
pledges to reduce GHG emissions, the Paris Agreement goals will not be 
met. Indeed, the 2 °C goal could be reached between 2050 and 2060 and 
the 1.5 °C goal could be reached by the early 2030s. 


