The evidence for the human impact on Earths climate is abundant and incontrovertible, based on our understanding of underlying concepts of the physics of our Earth system and on abundant direct and indirect observations (though its true that the details can get pretty complicated).
it has been known since the late 19th century that certain ‘greenhouse’ gases would warm climate, and burning fossil fuels emits these gases
since late 1960s concern about this caused fossil fuel companies, governments and academics to study the problem more intensely
recognition of the scale of the problem and that it doesn’t care about international borders led to the formation of the Intergovernmental Panel on Climate Change to collect and present the information to governments to aid their informed decision making
in 2021, even the World Economic Forum put climate change and environmental degradation at the top of its global risks
Despite this, “ever since scientists first began to explain the evidence that our climate was warming – and that humans activities were probably to blame – people have been questioning the data, doubting the evidence, and attacking the scientists who collect and explain it.“ Naomi Oreskes and Erik Conway in Merchants of Doubt
Why is that so? Why is it so hard to convince people of something that is as certain as our knowledge that smoking cigarettes can damage your lungs and potentially cause cancers? Here are some of my thoughts on this point:
history of the potential system forcings (e.g. greenhouse gases, solar activity, volcanism)
a model connecting 1 and 2 (can be simple or a complex numerical representation of real world physics)
estimate of magnitude of internal variability of the system (the “noise”)
By running the model with the different possible forcing factors as inputs, and then comparing the model output to the observations we can see to which forcing we can most reasonably attribute the observations. This is nicely illustrated in this figure from the IPCC Special Report on Ocean and Cryopshere in a Changing Climate
The food-energy-water nexus refers to the way that water security, energy security and food security (all vital for human well-being, poverty reduction and sustainable development) are strongly linked to one another, so the actions in any one area often have effects in one or both of the others:
Source: IWA, 2018. Sustainable Development: The Water-Energy-Food Nexus.
While almost 800 million people are currently hungry, by 2050 global food production would need to increase by 50% to feed the more than 9 billion people projected who live on our planet (FAO/IFAD/UNICEF/WFP/WHO, 2017).
72% of all water withdrawals are used by agriculture, 16% by municipalities for households and services, and 12% by industries. (UN-Water 2021)
It typically takes between 3,000 and 5,000 litres of water to produce 1 kg of rice, 2,000 litres for 1kg of soya, 900 litres for 1kg of wheat and 500 litres for 1kg of potatoes. (WWF).
In sub-Saharan Africa, irrigated areas are expected to more than double by 2050, benefiting millions of small-scale farmers. However, it has been estimated that 41% of current global irrigation water use occurs at the expense of environmental flow requirements. (FAO 2020)
The food production and supply chain accounts for about 30% of total global energy consumption. (FAO, 2011)
90% of global power generation is water-intensive. (UN, 2014)
Power plant cooling is responsible for 43% of total freshwater withdrawals in Europe (more than 50% in several countries), nearly 50% in the USA, and more than 10% of the national water cap in China. (UN, 2014)
Global water demand (in water withdrawals) is projected to increase by 55% by 2050, mainly because of growing demands from manufacturing (400% increase). (OECD, 2012)
The Paris Agreement which came into force in 2016 is a legally binding agreement in which almost all nations of the world agreed to put in place policies to keep global climate warming to below 2°C and ideally below 1.5°C above pre-industrial levels. The 2018 IPCC Special Report on Global Warming of 1.5°C, that was commissioned as a result of the Paris meeting concluded that:
The report finds that limiting global warming to 1.5°C would require “rapid and far-reaching” transitions in land, energy, industry, buildings, transport, and cities. Global net human-caused emissions of carbon dioxide would need to fall by about 45 percent from 2010 levels by 2030, reaching ‘net zero’ around 2050. This means that any remaining emissions would need to be balanced by removing CO2 from the air.
This is obviously an incredible challenge. Even a global pandemic and associated ‘shut down’ of some sectors of economic activity only caused a small blip in global emissions, as described in this article.
So what human activities are producing greenhouse gases?
Where can we focus our efforts?
And what about the social justice aspect?
Emissions are currently quite strongly related to GDP, so how can we reduce our emissions while still fulfilling peoples life aspirations?