Long term “global warming” is “increasing global energy”. This is the one thing we know, that total energy the earth is capturing from the sun is increasing. The earth is a very complex system and so we are doing an experiment to find out what happens when the earth retains more of the sun’s transmitted energy. The major effect is a warming of the earth, but this will not be even across the globe, in fact in the UK warming of the planet may change the Gulf Stream ocean current and over time make the UK considerably cooler (Newfoundland climate).
Climate Change has been adopted as a more appropriate term to describe what is happening, but we still refer to the cause of the change as being the increase in greenhouse gases (GHGs). GHGs in the atmosphere cause more energy from the sun to be retained by the earth with less energy being radiated into space. The main GHG is carbon dioxide, but other gases also act to insulate the earth.
The graph below shows the increase in global temperature between 1880 and 2010, with a nearly 1 degree rise in surface temperature caused by the 100ppm (part per million) increase in CO2 in the atmosphere.
CO2 is essential for life on earth, with plants photosynthesising CO2 to allow them to grow and to provide food for animals. For the earth’s climate to be stable we need the level of GHG gases in the atmosphere to remain constant, which is the case when the earth (sea / permafrost / rocks / humans / animals / etc) emit as much GHGs as is being absorbed through photosynthesis, formation of carbonate minerals, absorbed in the oceans. This balance is net zero CO2 for the whole world and was the state the world was in for millennia, but this was changed by fossil fuel driven industrialisation.
The global population needs to get to net zero carbon dioxide emission to stop the earth continuing to absorb more and more of the sun’s energy, so stopping the earth getting ever hotter. The Paris Climate Convention agreed to limit temperature rise to 1.5 degrees. The alternative to do nothing would be a huge experiment, which theoretical models suggest would be a disaster, increased sea level, longer droughts, stronger storms, more wildfire, etc.. There is a significant risk that the models are wrong and as the temperature rises other mechanisms may change the climate even more drastically, change in ocean currents, release of methane from permafrost. The 1.5 degree rise will be difficult to adapt to across the globe, higher levels of temperature rise may be impossible to adapt to, making significant populated areas of the world uninhabitable.
Industrialisation based on wood or hydropower may cause pollution / land damage but will not directly increase CO2 emissions. With trees being continually grown and burnt, so CO2 is captured by the tree then released when it is burnt and then captured when a new tree is grown. The use of fossil fuels gave us access to high density energy source, but when burnt the CO2 adds to the concentration in the atmosphere as there is no capture built in and the CO2 emitted by fossil fuels was captured by trees which grew over millions of years.
Carbon dioxide caused by burning fossil fuels is the major GHG, as it stops the earth emitting heat back into space. Other gases are also GHGs, often people talk about CO2 equivalent CO2e, so methane is 20 times more warming as CO2, and CFCs/HCFCs (refrigerants) are 1000s times more warming.
The pie chart shows roughly where CO2 came from in 2016 – burning for fossil fuels for energy account for over 70% of the emissions when used in industry, transport, heating buildings, 18% from agriculture/forestry/land use/, 3% from waste and 5% from industry – cement/chemicals
Getting to net zero will not reduce the amount of GHGs already in the atmosphere and so any increases in global temperature will at least remain. The Paris Climate Conference set a limit of 2 degrees warming over pre-industrial levels, effectively setting a limit to the amount of GHGs which can be released. However, 2 degrees warming means the climate will have been changed and hence we will still need to live with/mitigate the effects in different parts of the world (bush fires in Australia, more typhoons, more cyclones, colder winters, warmer summers, …).
Globally net zero carbon is a realistic target, but as human release of GHGs is overwhelming the environmental factors which had kept the global GHGs level relatively constant for millennia, net zero is not feasible with “business as usual“. “Business as usual” means we would continue to waste energy and waste materials (embedded GHGs), and keep planting more and more trees to absorb CO2 to compensate for the continued GHGs release, but the earth is finite. If we are to stop wasting energy and wasting materials then business will need to change, we could invent technologies which with entirely circular manufacturing disconnect growth from increased GHGs production and/or we change our lives/business so that we don’t continue to release GHGs.
“Business as usual” relies on the burning of fossil fuels which is the biggest source of CO2 emissions (>70%), but major businesses are based on the exploitation of fossil fuels. It is thus not surprising that there has been much talk of carbon capture and storage (CCS), where the CO2 from burning is captured from the waste gases and typically pumped underground to be stored forever. If all CO2 could be captured and even existing CO2 sucked from the atmosphere, then business as usual could continue, but this is currently just a magic CO2 tree. Capture of CO2 may well be a small part of the path to net zero, but currently the energy and equipment needed to capture/compress/store the CO2 is significant while the energy needed may reduce it will need to be compensated for by increased energy use most likely from more fossil fuel extraction.
The temperature of the earth has increased by more than 1 degree from pre-industrial levels with consequent effects on the earth’s climate. At the Paris Climate Conference the attendees concluded that 2 degrees increase would result in catastrophic climate change, and countries agreed to do everything possible to limit temperature rise to less than 1.5 degrees. 2 degrees is so bad as many tipping points for the earth’s climate would have been exceeded, such as changes in ocean current, release of methane trapped at the bottom of the oceans, melting of permafrost, drying up of peatlands, …….