In a new paper about accelerated ice loss in Antarctica, Rignot et al. (2019) list the three ways: 1. the component method in which whatever data on ice and snow amounts are available at the finest resolution possible, from the smallest areas studied areas (as little as 100 meters, ranging up to 1km) are collected then added up for as many years as they are available, and the trend plotted; 2. The altimetry method which, I presume, uses satellite altimetry to figure out how much ice and snow are present based on the height above ground and sea is measured…this has a spatial resolution of 1-10km; and 3. The gravity method (probably using the Grace satellite pairs to measure gravity changes over time owing to ice loss. The latter method can resolve centimeter-level losses but at a low resolution of 333 km. The latter two methods are relatively easy…just process satellite data…or maybe not so easy but relatively so. The component method is labor intensive, but better at pinpointing areas of loss which facilitates trying to understand what is causing the loss. Rignot used the component method.
Their results, reported widely in the news media, should be chilling. The climate-change enhanced westerly winds in the southern hemisphere are evidently pushing relatively warm circumpolar deep water (CDW) up against the edges of the ice sheets over much of the continent and increasing their melting and calving of icebergs at much higher rates than in previous decades. The loss of ice not only increases sea level faster than anyone had thought, it allows glaciers to flow into the sea faster as well, speeding the whole process.
Not that this comes as too much of a surprise to those of us who have been following global warming, but considering the exacerbated coastal flooding that is becoming commonplace, it might be good to point out to the climate change deniers inhabiting the higher levels of our government.
That is the assertion of a paper in Nature by Carolyn W. Snyder (Snyder, 2016) based on an analysis of the correlation between atmospheric CO2 concentrations and changes in the global average surface temperature (GAST) over the past 800,000 years. Actually the assertion is that the 95% “credible interval” is 7 to 13 degrees Celsius (12.6 to 23 degrees Fahrenheit) Yikes! Even the current scientific consensus value of something on the order of 3 C (5.4 F) (Collins et al., 2013) is frightening when you consider that the difference in the GAST between the last glacial maximum about 20,000 years ago and at present wasn’t much different than that. Continue reading →
A recent paper discussed in the previous post (Galbraith and Eggleston, 2017) claims that during the past 800,000 years when the Earth has been in a glacial condition with the occasional interglacial period (such as now), there is a strong correlation between global temperature and atmospheric CO2 levels, and that they tend to go to the same low point again and again and stay there. These authors argue that if CO2 were to go lower, so would the temperature, and that therefore something is keeping the CO2 level from going any lower then 190 ppm. One intriguing possibility they bring up comes from a paper (Pagani et al., 2009) by Mark Pagani at Yale, and his colleagues at the Carnegie Institution in Stanford and at the University of Sheffield who claim that plants stop effective photosynthesis if CO2 levels fall below 190 ppm, depriving the carbon cycle of two sources of removal of atmospheric CO2; photosynthesis, and a more subtle plant activity called biologically enhanced silicate chemical weathering. The mechanisms of these two processes are interesting. Continue reading →
Atmospheric CO2 levels are always lower during glacial periods than during interglacials like the one we are in now. During the last glacial maximum 20,000 years ago, for example, they were at 190 parts per million (ppm), whereas during the most recent 10,000 years, almost up to the present, they have been about 280 ppm. [We have now succeeded in raising them to over 400 ppm and still counting, but that’s a different story.] Eric Galbraith and S. Eggleston (Galbraith and Eggleston, 2017) argue that as far as we know, atmospheric CO2 levels have never gone below the typical glacial levels of 190 ppm, even in extended snowball earth conditions. Why not? Well, a carefully-reasoned 2009 paper they cite (Pagani et al., 2009) suggests that even in the mostly warm conditions of the last 24 million years, when CO2 levels fell below 190 ppm, terrestrial plants stopped effectively photosynthesizing, thus they not only stopped removing CO2 from the atmosphere directly, but they also stopped the active root growth which increases the acidity of soils and enhances chemical silicate weathering from the rocks which removes CO2 from the soil, and ultimately from the atmosphere. Galbraith and Eggleston argue that the same thing has been happening during the glacial periods of the last 800,000 years, and extend the argument to the photosynthesis of oceanic phytoplankton. To wit, when CO2 levels get below 190 ppm, CO2 removal from the atmosphere by photosynthesis and chemical weathering is sharply reduced, so they decline no further. Continue reading →
Seidler and Stevenson (2017) review two books dealing with the psychological factors that impact the personal and societal undervaluing of humanity’s role in causing climate change and its effects on them. They stress that this is not a new issue: even in 1988 the Intergovernmental Panel on Climate Change (IPCC) emphasized the need for a systemic change in energy production and consumption. Almost 30 years later, CO2 emissions have more than doubled, and it is still unclear whether current efforts such as the Paris Conference (COP) will lead to meaningful action.
The two books, What We Think About When We Try Not to Think about Global Warming and Stolen Future, Broken Present: The Human Significance of Climate Change suggest that our inaction is caused not by a data gap or lack of understanding of the risks but our “psychic habits, social dynamics, and ethical quirks”. In the first book, author Stoknes discussed the need for effective marketing. While studies show that “scary” emotional marketing tactic is successful among almost all audiences, Stoknes poses some important questions about the role of marketing and persuasion: is the societal denial of climate change a result of too few messages? What is the balance between sufficient advertisement and evoking denial and rationalization? Are we presenting enough range of marketing tactics to engage everyone? Continue reading →
It is well known that fire can play a crucial role in the reproduction and development of plant populations. The availability of water and CO2 also impact plant growth, especially of larger species. It is believed that the interactions of climate, fire, and CO2 greatly influence the shift between savanna and tropical forest ecosystems and their permanence thereafter. Previous research has relied on data collected from intact tropical forests, but although useful, these data only provide a snapshot of the impact of CO2, fire, and climate on these ecosystems. To gain a better understanding of what factors influence tropical ecosystems Shanahan et al. (2016) used the concentrations of carbon and hydrogen stable isotopes from sedimentary leaf wax n-alkanes (δ13Cwax and δDwax) and the frequency of charcoal layers from sediment obtained from Lake Bosumtwi in Ghana to construct a history of changes in vegetation and hydrology, as well as to estimate the annual fire frequency. Continue reading →
When did the first ice on Earth occur? About the only way to find out is to find old rocks with evidence of glaciation then determine exactly how old they are. A type of rock characteristic of glaciation is diamictite, a conglomerate-like mix of rocks with a large range of sizes held together with clay or mud that has been metamorphosed into mudstone. The large range of intermixed sizes in these deposits indicates lack of the size sorting that occurs in a river bed or floodplain, so some other source of disruption must have occurred, one of which is being scraped off and bulldozed along by a glacier. David Zakharov at the University of Oregon with a team of scientists from around the world (Zakharov et al., 2017) reasoned that if they could find examples of this type of rock that had formed near the equator, and could demonstrate that the water the rock encountered during formation came from glacial meltwater, then, they would have proven that at the time there were glaciers near the equator. Continue reading →