Orbital changes are responsible for Milankovitch cycles that make Earth move in and out of periods of glaciation, or Ice Ages. Summer insolation on the Northern Hemisphere reached a peak some 10,500 years ago, in line with the Milankovitch cycles, and insolation has since gradually decreased.
|Summer insolation on the Northern Hemisphere in red and in langleys
per day (left axis, adapted from Walker, 2008). One langley is 1 cal/cm²
(thermochemical calorie per square centimeter), or 41840 J/m² (joules
per square meter), or about 11.622 Wh/m² (watt-hours per square meter).
In blue is the mean annual sea surface temperature, given as the difference
from the temperature over the last 1000 years (right axis, from Bova, 2021).
Snow and ice cover acting as a buffer
While temperatures rose rapidly, especially before the insolation peak was reached, the speed at which temperatures rose was moderated by the snow and ice cover, in a number of ways:
- snow and ice cause sunlight to get reflected back into space
- energy from sunlight is consumed in the process of melting snow and ice, and thawing permafrost
- meltwater from sea ice and runoff from melting glaciers and thawing permafrost cools oceans.
In other words, the snow and ice cover acted as a buffer, moderating the temperature rise. While this buffer has declined over time, it is still exercizing this moderation today, be it that the speed at which this buffer is reducing in size is accelerating, as illustrated by the image below, showing the rise of the sea surface temperature on the Northern Hemisphere.
|[ from earlier post ]|
Will the snow and ice cover ever grow back?
More recently, the temperature rise has been fueled by emissions caused by people. While emission of greenhouse gases did rise strongly since the start of the Industrial Revolution, the rise in emission of greenhouse gases by people had already started some 7,000 years ago with the rise in modern agriculture and associated deforestation, as illustrated by the image below, based on Ruddiman et al. (2015).
The temperature has risen accordingly since those times. At the start of the Industrial Revolution, as the image at the top shows, temperatures already had risen significantly, compared to some 6000 years before the Industrial Revolution started. When also taking into account that the temperature would have fallen naturally (i.e. in the absence of these emissions), the early temperature rise caused by people may well be twice as much.
Temperatures could keep rising for many years, for a number of reasons:
- Snow & Ice Cover Loss – A 2016 analysis by Ganapolski et al. suggests that even moderate anthropogenic cumulative carbon dioxide emissions would cause an absence of the snow and ice cover in the next Milankovitch cycle, so there would be no buffer at the next peak in insolation, and temperatures would continue to rise, making the absence of snow and ice a permanent loss.
- Brighter Sun – The sun is now much brighter than it was in the past and keeps getting brighter.
- Methane – Due to the rapid temperature rise, there is also little or no time for methane to get decomposed. Methane levels will skyrocket, due to fires, due to decomposition of dying vegetation and due to releases from thawing of terrestrial permafrost and from the seafloor as hydrates destabilize.
- No sequestration – The rapidity of the rise in greenhouse gases and of the associated temperature rise leaves species little or no time to adapt or move, and leaving no time for sequestration of carbon dioxide by plants and by deposits from other species, nor for formation of methane hydrates at the seafloor of oceans.
- No weathering – The rapidity of the rise also means that weathering doesn't have a chance to make a difference. Rapid heating is dwarfing what weathering can do to reduce carbon dioxide levels.
- Oceans and Ozone Layer Loss – With a 3°C rise, many species including humans will likely go extinct. A 2013 post warned that, with a 4°C rise, Earth will enter a moist-greenhouse scenario. A 2018 study by Strona & Bradshaw indicates that most life on Earth would disappear with a 5°C rise. As temperatures kept rising, the ozone layer would disappear and the oceans would keep evaporating and eventually disappear into space, further removing elements and conditions that are essential to sustain life on Earth.
All this has implications for the interpretation of the Paris Agreement. At the Paris Agreement, politicians pledged to take efforts to ensure that the temperature will not exceed 1.5°C above pre-industrial levels.
So, what is pre-industrial? To calculate how much the temperature has risen, let's start at 2020 and go back one century. According to NASA data, the temperature difference between 1920 and 2020 is 1.29°C (image below).
The NASA ocean data are for sea surface temperatures, so another 0.10°C can be added to obtain global air near surface temperatures (2 m). Furthermore, it makes sense to add another 0.10°C for higher polar anomalies. This would bring the temperature rise from 1920 up to 1.49°C.
Of course, 1920 is not pre-industrial. As the IPCC mentions, the 'pre-' in pre-industrial means 'before', implying that 'pre-industrial' refers to levels as they were in times well befóre (as opposed to when) the Industrial Revolution started.
When taking the rise over the past century and adding 0.30°C for the rise over the previous 170 years, that brings the rise up to 1.79°C (from ≈1750, the start of the Industrial Revolution). Carbon dioxide and methane levels started to rise markedly about 6000 years ago, causing a 0.29°C rise for the years from 3480 BC to 1520 (see image at top). Finally, there will also have been a rise for the years from 1520 to 1750 that, when estimated at 0.20°C, would mean that emissions by people could have caused the temperature to rise by 2.28°C (4.122°F), compared to the temperature some 5500 years ago (see inset on above image).
A huge temperature rise by 2026?
A recent post suggests that the 1.5°C threshold was already crossed in 2012, i.e. well before the Paris Agreement was adopted by the U.N. (in 2015), while there could be a temperature rise of more than 3°C by 2026.
Such a rise could be facilitated by a number of events and developments, including:
|[ from earlier post see CH4 GWP]|
• The Arctic sea ice latent heat tipping point and the seafloor methane hydrates tipping point look set to get crossed soon (see above image).
• Continued emissions. Politicians are still refusing to take effective action, even as greenhouse gas emissions appear to be accelerating. The warming impact of carbon dioxide reaches its peak a decade after emission, while methane's impact over a few years is huge.
• Sunspots. We're currently at a low point in the sunspot cycle. As the image on the right shows, the number of sunspots can be expected to rise as we head toward 2026, and temperatures can be expected to rise accordingly. According to James Hansen et al., the variation of solar irradiance from solar minimum to solar maximum is of the order of 0.25 W/m⁻².
• Temperatures are currently also suppressed by sulfate cooling, and their impact is falling away as we progress with the necessary transition away from fossil fuel and biofuel, toward the use of more wind turbines and solar panels instead. Aerosols typically fall out of the atmosphere within a few weeks, so as the transition progresses, this will cause temperatures to rise over the next few years.
• El Niño events, according to NASA, occur roughly every two to seven years. As temperatures keep rising, ever more frequent strong El Niño events are likely to occur. NOAA anticipates the current La Niña to continue for a while, so it's likely that a strong El Niño will occur between 2023 and 2025.
• Rising temperatures can cause growth in sources of greenhouse gases and a decrease in sinks, as discussed in an earlier post.
The mass extinction event that we are currently in is rapidly progressing, even faster than the Great Permo-Triassic Extinction, some 250 million years ago, when the temperature rose to about 28°C, i.e. some 14.5°C higher than pre-industrial.
In the video below, Guy McPherson discusses the current mass extinction.
In the video below, Ye Tao introduces and discusses the MEER ReflEction idea.
In conclusion, there could be a huge temperature rise by 2026 and with a 3°C rise, humans will likely go extinct, which is a daunting prospect. Even so, the right thing to do is to help avoid the worst things from happening, through comprehensive and effective action as described in the Climate Plan.
• Climate change and ecosystem response in the northern Columbia River basin – A paleoenvironmental perspective – by Ian R. Walker and Marlow G. Pellat (2008)
• Vance, R.E. 1987. "Meteorological Records of Historic Droughts as Climatic Analogues for the Holocene." In N.A. McKinnon and G.S.L. Stuart (eds), Man and the Mid-Holocene Climatic Optimum – Proceedings of the Seventeenth Annual Conference of the Archaeological Association of the University of Calgary. The University of Calgary Archaeological Association, Calgary: 17-32.
• Seasonal origin of the thermal maxima at the Holocene and the last interglacial – by Samantha Bova et al. (2021)
• Palaeoclimate puzzle explained by seasonal variation (2021)
• Important Climate Change Mystery Solved by Scientists (news release 2021)
• Milankovitch (Orbital) Cycles and Their Role in Earth's Climate – by Alan Buis (NASA news, 2020)
• Milankovitch cycles – Wikipedia
• Insolation changes
• Late Holocene climate: Natural or anthropogenic? – by William Ruddiman et al. (2015)
• Critical insolation–CO2 relation for diagnosing past and future glacial inception – by Andrey Ganapolski et al. (2016)
• Co-extinctions annihilate planetary life during extreme environmental change – by Giovanni Strona & Corey Bradshaw (2018)https://www.nature.com/articles/s41598-018-35068-1
• Earth is on the edge of runaway warminghttps://arctic-news.blogspot.com/2013/04/earth-is-on-the-edge-of-runaway-warming.html
• Paris Agreement
• IPCC Special Report: Global warming of 1.5 ºC — Box SPM.1: Core Concepts https://www.ipcc.ch/sr15/chapter/spm/
• IPCC AR5 Synthesis Report — Figure 2.8
• IPCC AR5 Report, Summary For Policymakers
• NASA Analysis Graphs and Plots – LSAT and SST changehttps://data.giss.nasa.gov/gistemp/graphs_v4/
• Most Important Message Ever
• Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing – by M. Etminan et al.
• When Will We Die?
• Possible climate transitions from breakup of stratocumulus decks under greenhouse warming – by Tapio Schneider et al.
• A World Without Clouds
• How close are we to the temperature tipping point of the terrestrial biosphere? – by Katharyn Duffy et al.https://advances.sciencemag.org/content/7/3/eaay1052
• What Carbon Budget? https://arctic-news.blogspot.com/2021/01/what-carbon-budget.html
• 2020: Hottest Year On Record
• Overshoot or Omnicide?https://arctic-news.blogspot.com/2021/03/overshoot-or-omnicide.html
• Confirm Methane's Importance
• Arctic Ocean invaded by hot, salty water https://arctic-news.blogspot.com/2021/05/arctic-ocean-invaded-by-hot-salty-water.html
• Greenhouse gas levels keep rising at accelerating rates
• CH4 GWPhttps://arctic-news.blogspot.com/p/ch4-gwp.html
• Climate Plan