We simply cannot ignore the greatest threat to us all.
A lot has been said and written about humankind-generated, now often called anthropogenic, climate change. While many people are concerned about this, some are sceptical or deny its reality, preferring to think of it as a conspiracy and/or an anti-western/capitalist anarchistic plot. As an astronomer I think it may be helpful to offer an explanation of how global warming is happening, and why the deniers are wrong.
In my opinion, global warming and the melting of the Earth’s ice sheets is a bigger problem than the Covid-19 pandemic currently afflicting us – it will eventually affect more people. A higher frequency of ‘extreme’ weather events will be seen; resource shortages (especially water and agricultural land/food) will lead to mass population migrations; and conflicts over such natural resources (rather than the historical oil-based conflicts) will occur. Assessments made by the University of London (Royal Holloway) show that almost a quarter of the world’s population relies upon glacier melt water for drinking and agriculture needs.Global ice acreage, as reported by the National Snow and Ice Data Center (NSIDC), and permafrost melt (together with releases of high levels of stored CO2 and methane), is accelerating at an alarming rate, as reported by the American Geophysical Union (June 2019). These are macro and global political problems that need urgent attention.
Historical (pre-instrumentation) global temperature measurements are assessed by using proxies such as tree-rings, ice core, ocean sediment, and coral development analyses. These analyses have shown that global temperature over the past 1000 years has been consistently lower than the 20th and 21st centuries (eg Mann-Bradley 1998 & Wahl-Ammann 2007). Indeed, there is evidence of a gradual cooling and periods of prolonged cold. Europe experienced the ‘little ice age’ in the late 15th century, and frost fairs were held on the frozen river Thames in the 17th and 18th centuries. However, from the mid-19th century global temperature has risen broadly in line with coal usage and the industrial revolution. Alarmingly, the rise in temperature has accelerated since the early 20th century and today we are seeing a sustained upward climb.
But global temperatures are not particularly useful when looking at polar and glacial environments. The problem with a global measurement is that, by necessity, it is a global average. While the global temperature has risen by just under 1°C over the past 150 years, the temperature in the high latitude Arctic (60°N to 90°N) has risen by 2.4°C. The shockingly high temperature recorded of 37.7°C in Verkhoyansk in North Eastern Siberia (at latitude 67.5° N) on the 23rd of June was not a one-off. The region had been sweltering under the hottest May temperatures ever recorded in the region.
The science behind global warming is complicated. Atmospheric physics is progressed and understood through large scale thermal, chemical and fluid dynamics mathematics; and often numerical modelling (mathematical simulations) are the only mechanisms available to provide forecasts. The atmosphere is a prime example of a chaotic (in the mathematical sense) system and very small changes in modelling parameters/initial conditions can result in large variations in long-term results. However, trends can be determined, and we have a good understanding of the fundamental processes in operation.
Solar Radiation and Thermal Equilibrium
There are two major processes which affect global temperature: the amount of heat we receive from the Sun; and the amount of heat retained within our atmospheric ‘blanket’. We will examine only the first of these here – how sea ice, the polar ice caps and mountain glaciation are critical for global temperature equilibrium (balance).
If an object receives more energy than it reflects or radiates it will get hotter. When we come inside on a cold day we warm to the temperature of the room, and the internal heat we need to generate chemically within our bodies reduces. We don’t overheat because our bodies become heat-balanced with the room. Except for gravitational potential and orbital energy (which do not affect global temperature), all the energy received by the Earth’s atmosphere and surface, is from the Sun.
The energy received from the Sun into the Earth’s atmosphere is called the solar irradiance. This is very stable/consistent (see observatoire solaire). Although very small short term variations are seen in the solar irradiance through the slight eccentricity of the Earth’s orbit, and through the approximately 11-year solar cycle, these do not and cannot account for the atmospheric and sea temperature rises observed. The long-term cyclical changes in the Earth’s orbital and rotation, collectively termed the Milankovitch cycles, are often wilfully misconstrued and misquoted by deniers of anthropogenic climate change. The Milankovitch cycles have 26,000 to 100,000 year elemental variations and are irrelevant as far as the climate changes observed over the past 200 years are concerned.
Global Albedo and Ice Reduction
Some sunlight (or, specifically, the spectrum of radiation we receive from the Sun, i.e. visible, infrared, ultra-violet etc wavelengths) is reflected by the Earth’s atmosphere, including clouds, and the surface and is not absorbed. It is reflected back into space and does not contribute to the temperature of the Earth.
The amount (proportion) of light an object reflects is call the albedo of the object. The Earth is a relatively shiny planet and reflects about 30 to 35 % of the sunlight incident upon it. The Moon is duller and reflects a more consistent 12% of incident sunlight.
Dark rocks such as granite and charcoal have albedos typically around 15% and 4% respectively. Fresh snow is very reflective at circa 90%. Sea water is dull at about 6%, while sea ice varies from 50 to 70%. So, the duller an object, the more heat it absorbs. The problem we have is that the reduction in area (by melting) of the ice caps, sea ice and mountain region glaciation is reducing the global albedo by both reducing the reflective ice surfaces and exposing more of the much less reflective sea surface or rocky land beneath. This means that our planet is no longer in thermal equilibrium (heat balance) and our atmosphere is heating up.
It is analogous to us living in a greenhouse. We have reflective foil on our roof which means our greenhouse doesn’t heat up too much. But what is happening now is that our reflective foil (ice) is being removed, and all the dark surfaces within are now absorbing heat. So, we’re heating up. And life in our greenhouse will change.
This is why ice is so important to us. And why we need to be both very worried and active in every way we can to ensure we do not continue to compromise our icy regions. To put this in context, 1.36 million square kilometres of Arctic sea ice has been lost since 1979 (according to NSIDC); this is over 10 times the area of England, and over 10% of the current Arctic sea ice area. The loss of ice shelves within western Antarctica is similarly worrying.
The second major process governing global warming is retention of heat. Retained heat is rather sensitive to atmospheric chemistry, with water vapour; carbon dioxide; and heavier ‘greenhouse’ gasses such as methane all adding to heat retention. We will each have heard lots on these latter processes. In our greenhouse analogy, not only have we ripped down our reflective foil, but we’ve decided to put a warm coat on too! There is very much more to say on many atmospheric aspects. But albedo, and ice, are critical.
What Can I Do to Help?
Plenty! We have seen during the Covid-19 pandemic lockdowns in many countries how the environment and atmosphere can make a remarkable ‘recovery’. The NO2 and particulate levels within our towns and cities have plummeted; water courses have become cleaner (the canals of the city of Venice are a clear example of this); and the emissions of CO2 and other atmospheric pollutants have dropped substantially. We need to sustain these healthier conditions.
Climate Change Politics
Sadly, our governments are not doing enough to counter the very real threats of climate change. Despite former PM Theresa May’s pledge to commit to a zero-carbon emission economy by 2050, our national commitment to this is not evident (unearthed.greenpeace.org/2020) The ‘welcoming’ of the reduction in Arctic ice as a means to enable sea routes for trading, as cited by the US secretary of state as a reason for not signing the 2019 Arctic Accord (bbc.co.uk/news); and the open adoption of these routes for trade by the UK Dept. of Transport www.gov.uk) does not bode well for our future.
Hence, in addition to our personal actions, one thing we can all do is to keep on at our respective governments about this. The group Extinction Rebellion has made the headlines, often for the wrong reasons, making a lot of their direct action counter-productive; as has the campaigning work of Greta Thunberg. We each have views of such activists, but I believe that the evidence indicates that their underlying cause is ‘correct’ and needs personal, political and global attention.
Please help keep sustainability and environmental priority high on your political representatives’ agenda.