It has been claimed that climate change is a recent and unique process which threatens the basic survival of humanity.
But how does the current profile of climate change correlate to the very long picture of climate on the planet?
This paper presents a graphical representation of the issues of increasing atmospheric CO2, global warming, climate change and rising sea level over a very long time period.
Initially, the increase in atmospheric CO2 over the past century is put into context and related to the geological profile. Subsequently, the temperature record is observed together with the link to CO2 concentrations. Holocene climatic variations are observed, and considered in the light of a longer term geological climate picture. The impact of recent climate change and its attribution to greenhouse gas is observed. Finally the trends and impacts of sea level increases are noted and considered in avery broad temporal setting.
Fig 1. Atmospheric Carbon Dioxide
There has been a general public perception that CO2 levels have been rising strongly, especially over the later part of the last century, and this seems to be confirmed by the data.
Very reliable atmospheric CO2 measurements from Mauna Loa Hawaii since the late 1950s demonstrate a sustained increase in global CO2 concentrations over the past 50 years. Such concentrations are considered directly linked to global warming and are claimed to be attributable in part to human activity. The recent variations appear to be considerably in excess of the very long term (400,000 year) cycles of CO2 variation, which had seemed to peak in the order of 250 to 280 ppmv. The current concentrations are higher being in the order of 385ppmv. Fig 2.
Fig 2. CO2 Variations
In a geological context looking back to 500 million years, CO2 levels were as much as 20 times higher than currently. For much ot the past 200 million years the CO2 levels were in the order of 4 to 6 times higher than today. On most measures, the current CO2 concentrations are very close to planetary lows for the past 500 million years.
Fig 3. CO2 Profiles over 500 million years.
The dynamic economic growth of the past couple of centuries has been phenominal. This progress has not always come without certain costs. Global emissions from fossil sourced carbon have increased by nearly 3 orders of magnitude since 1750.
Fig 4. Fossil Sourced Carbon Emissions.
The major source of fossil sourced carbon emissions is petroleum, followed by coal and natural gas, all prime energy sources in the industrialising global economy.
Fig 5. Sources of Carbon
The major source of carbon emissions for the most part of the 20th century has been North America, but this region has recently been surpassed by China. Western Europe appears to have stabilised emissions over the past 30 years or so. The other significant recent change has been the rapid decline of emissions from Eastern Europe and the Soviet block generally.
Fig 6. Carbon Emissions by Regions.
The recent surface temperature record appears highly correlated to the CO2 concentration record. From time to time this record appears to be impacted by events such as significant volcanoes – Pinitubo in the early 90s – as well as broader climatic events such as El Nino (warmer) and La Nina (cooler).
Fig 7. Surface Temperature Record.
The constructed temperature record over the past 2 millennia shows the impact of the “little Ice Age” and the recent progress of increased CO2 concentrations. The current level of global temperatures is now beyond the highest boundary for the past 2000 years, Fig 8.
Fig 8. Reconstructed Temperature Record.
Long term records derived from Vostok Antarctic ice cores, illustrate the strong cyclical link between temperature variation, carbon dioxide concentrations, and possibly dust concentrations, over the past 400,000 years. An interesting feature of the record over the past 400,000 years has been the reasonably regular cycles which has seen a slow decline of CO2 over roughly 100,000 years to be interrupted by a very sharp spike in CO2. There have been five such spikes over the past 400,000 years and the Earth is currently in the vicinity of a spike which actually began in the order of 20,000 years ago.
Fig 9. Evidence from the Vostok Cores
During the recent Holocene period – which has coincided with the rise of human civilisation over the past 10,000 years, the planet has been experiencing a most benign and stable phase of climate (for humans anyway). Following an earlier glacial phase 12,000 years ago (Younger Dryas), the temperature record has actually been on a steady downward trend, although the temperature anomaly in 2004 at 0.5 was considerably above the trend (but it has since declined from this level). Most of the perturbations over the past 10,000 years are directly attributable to specific extraneous climate phenomena such as the Dansgaard Oeschger events or Bond events. This does not seem to be the case with the recent cycle of warming. It also should be remembered that the Dryas ice age cycle is about 12,000 years and is probably past due.
Fig 10. Holocene Temperature Variations.
The climate change record closely follows the temperature record. The record for the past 5.5 million years illustrates a general cooling of the planet (the variation is a measurement perspective phenomenon).
Fig 11. 5 Million Years of Cooling.
While there have been significant phases of climatic extremes over the past 550 million years, the strong recent trend over the past 100 million years has been a cooling trend. The big temperature – climate trend has in fact been a significant cooling phase.
Fig 12. The Long Term Trend of Global Cooling
Fig 13. Over the Long Term, Evidence of Global Cooling
The cooling trend is clearly seen over the past 60 million years, and has accelerated over the past 13 million years. Thus, the big picture of the very recent spike of CO2 and temperature increase, is that it has occurred in a phase of exceptionally low planetary temperatures, where the long term trend is in fact cooling.
Actual climate change attribution, since 1990, is dominated by the impact of greenhouse gas emissions. There is some small evidence of increasing solar attribution but the trend has been negativeb for volcanic and sulfate sources.
Fig 14. Climate Change Attribution
Since 1880 the rise in sea level has been about 20 cm. This appears to be in accord with the projections derived from increasing CO2 concentrations and temperature increases.
Fig 15. Sea Level Rises.
In the setting of the Holocene climatic change record the sea level increases are very modest. The most significant impact some 8,000 years ago saw sea levels rise 13 meters over about 1000 years. The sea level rise since has been as little as 3 metres over the remaining 8,000 years.
Fig 16. Sea Level Rises
In a very long geological time frame global sea levels have fluctuated some 450 metres and most notably the current global sea level is very close to the lowest levels for the past 550 million years. Sea levels were comparably as low as they currently, only 250 to 300 million years ago and then beyond 540 million years ago.
Fig 17. sea level fluctuations
Current projections of sea level rise by the end of this century are in the order of 2 to 3 meters. To put this in context, it is when sea levels rises get up to about 12 meters that impacts on the major centers of settlement on the Australian coastline (as it will all over the world), will become significant. However, in terms of lost land mass overall, such a sea level rise will not impact land area significantly. It is only when sea level rise gets to the order of 70 meters that major significant modification of the coastline does occur substantially.
The bottom line is that there is evidence of increasing concentrations of atmospheric CO2, as well as a small temperature spike. In the setting of geological time this recent incidence is barely a heartbeat in a lifetime, when the big temperature and climate trend is massively downward. The recent Holocene phase has proven to be exceptionally benign and has been a lull in the downward temperature trend.
The recent phase of increased CO2 emissions does appear to be an abnormal event in the current climate record over a very short phase of geological time. Increases in surface temperature and sea level seem to be correlated issues. In terms of a geological perspective of CO2, surface temperature, climate change and sea level, the planet does seem to be at a very low phase; CO2 concentrations, surface temperature, and sea level are at very long term lows. Despite the heuristic propensity to expect all of these to rise, it is also the case that the expectation of a Dansgaard Oeschger event or certainly a Dryas type event is rather high.
A Big Picture of Climate Change
By Dr. A. K. Dragun (August 2012)