climate modelling – Olduvai.ca

Draft script:

From Popular Mechanics comes this headline on 22 April 2024: Trillions of Tons of Carbon Are Missing from Climate Models. The story begins with three bullet points: (1) While the world’s soils are home to lots of organic carbon—such as leaf litter and animal waste—inorganic carbon, which is often in the form of solid carbonates, can also leak into the atmosphere. And it isn’t accounted for by current climate models; (2) A new study focuses on the role of soils as both a storage for and emitter of carbon, and found that 23 billion [metric] tonnes of inorganic carbon could escape soil over the next 30 years; and (3) Good land management—as well as other practices, such as afforestation and improved rock weathering—can help slow down this significant source of CO₂.

Here’s the lede: “The sole purpose of people and programs combating climate change is finding ways to keep carbon out of the atmosphere.” The first paragraph continues: “Planting trees is a big help, as their woody roots lock away carbon for decades, and companies are hard at work trying to find artificial means of sucking greenhouse gasses from the air and sequestering it underground. But in this obsession with tracking CO₂ levels, one significant source of both emission and storage has been overlooked—the soil.” A minor detail is worthy of mention: Planting trees is not necessarily a big help, as I pointed out previously in this space.

The article goes on: “the top two meters of soil beneath our feet currently hold roughly 2.3 trillion [metric] tonnes of inorganic carbon—five times more than all of the terrestrial plants on Earth combined.”…

…click on the above link to read the rest of the article…

Climate models can’t explain 2023’s huge heat anomaly — we could be in uncharted territory

May 14, 2024

Climate models can’t explain 2023’s huge heat anomaly — we could be in uncharted territory

Taking into account all known factors, the planet warmed 0.2 °C more last year than climate scientists expected. More and better data are urgently needed.

When I took over as the director of NASA’s Goddard Institute for Space Studies, I inherited a project that tracks temperature changes since 1880. Using this trove of data, I’ve made climate predictions at the start of every year since 2016. It’s humbling, and a bit worrying, to admit that no year has confounded climate scientists’ predictive capabilities more than 2023 has.

For the past nine months, mean land and sea surface temperatures have overshot previous records each month by up to 0.2 °C — a huge margin at the planetary scale. A general warming trend is expected because of rising greenhouse-gas emissions, but this sudden heat spike greatly exceeds predictions made by statistical climate models that rely on past observations. Many reasons for this discrepancy have been proposed but, as yet, no combination of them has been able to reconcile our theories with what has happened.

Earth just had its hottest year on record — climate change is to blame

For a start, prevalent global climate conditions one year ago would have suggested that a spell of record-setting warmth was unlikely. Early last year, the tropical Pacific Ocean was coming out of a three-year period of La Niña, a climate phenomenon associated with the relative cooling of the central and eastern Pacific Ocean. Drawing on precedents when similar conditions prevailed at the beginning of a year, several climate scientists, including me, put the odds of 2023 turning out to be a record warm year at just one in five.

…click on the above link to read the rest of the article…

Cancellations Start for John Clauser After Nobel Physics Laureate Speaks Out About “Corruption” of Climate Science

July 24, 2023

Cancellations Start for John Clauser After Nobel Physics Laureate Speaks Out About “Corruption” of Climate Science

Cooling effect of clouds ‘underestimated’ by climate models, says new study

June 12, 2021

Cooling effect of clouds ‘underestimated’ by climate models, says new study

Cooling effect of clouds ‘underestimated’ by climate models, says new study

* * *

Clouds could have a greater cooling effect on the planet than climate models currently suggest, according to new research.

The paper, published in Nature Climate Change, aims to correct a “long-standing” and “unaddressed” problem in climate modelling – namely, that existing models simulate too much rainfall from clouds and, therefore, underestimate their lifespan and cooling effect.

The authors have updated an existing climate model with a more realistic simulation of rainfall from “warm” clouds – those that contain water only, rather than a combination of water and ice. They find that this update makes the “cloud-lifetime feedback” – a process in which warmer temperatures increase the lifespan of clouds – almost three times bigger.

The authors note that the newest generation of global climate models – the sixth Coupled Model Intercomparison Project (CMIP6) – predicts faster future warming than its predecessors. This is largely because the new models simulate a smaller cooling effect from clouds.

However, the lead author of the study tells Carbon Brief that fixing the “problem” in rainfall simulations “reduces the amount of warming predicted by the model, by about the same amount as the warming increase between CMIP5 and CMIP6”.

Due to this, he says that the key takeaway from the study is to “take the extra warming in CMIP6 with a grain of salt until some of the other known cloud problems are also fixed in the models”.

Cooling clouds

The impact of clouds on global temperature is a complex area of research that scientists have been working on for decades.

In a Carbon Brief guest post published in 2018, Prof Ellie Highwood – professor of climate physics in the Department of Meteorology at the University of Reading – explains how clouds can affect global temperatures:

…click on the above link to read the rest of the article…

New research on forests and oceans suggest projections of future warming may be too conservative, with serious consequences

January 31, 2021

New research on forests and oceans suggest projections of future warming may be too conservative, with serious consequences

How much will the world warm with ongoing fossil-fuel carbon emissions? It’s a big question that preoccupies policymakers and activists, with important discussions about when the world will hit two degrees, are we really on a path to four degrees of warming with current Paris commitments, and so on.

And the answer is that the world is likely to warm more than current projections, if two recently published pieces of research on the terrestrial and ocean carbon sinks are any guide.

Warming projections and carbon sinks. Future warming projections come from complex climate models, which combine historic data, current observations, equations that encompass current understandings of the bio-geo-physical processes, and some assumptions about processes where direct observation or modelling is more difficult.

About 30% of the carbon dioxide (CO2) that humans are pouring into the atmosphere mixes with the top layer of the ocean (making the water more acidic and posing a growing acidification threat to ocean life), about 30% is absorbed by the terrestrial biosphere (trees and plants), and about 40% stays in the air, heating the planet.

Assumptions about those processes in the future fundamentally affect projections of future warming. If these ocean and terrestrial carbon stores (or “carbon sinks”) become less efficient, then a greater proportion of human emissions will stay in the air, and warming will be faster than currently projected for a given level of emissions.

So the models make assumptions about these carbon stores:

For the terrestrial carbon sink, it has been observed that with more CO2, plants grow faster because there is more CO2 “food” for them to absorb. This is known as the “fertilisation effect”, and while there are highly divergent sink trajectories from Earth system models, the models “nevertheless agree on continued futures increases in sink strength due to the CO2 fertilisation effect.

…click on the above link to read the rest of the article…

Analysis: How ‘carbon-cycle feedbacks’ could make global warming worse

April 17, 2020

Analysis: How ‘carbon-cycle feedbacks’ could make global warming worse

Scientists making climate-change projections have to deal with a number of uncertainties.

The amount of global warming will depend on the magnitude of future emissions, which, in turn, depends on how society grows and develops. The rate of warming will also depend on how sensitive the climate is to increased atmospheric greenhouse gases.

Yet climate change also depends on an under-appreciated factor known as “carbon-cycle feedbacks”. Accounting for uncertainties in carbon-cycle feedbacks means that the world could warm much more – or a bit less – than is commonly thought.

The carbon cycle is the collection of processes that sees carbon exchanged between the atmosphere, land, ocean and the organisms they contain. “Feedbacks” refer to how these processes could change as the Earth warms and atmospheric CO2 concentrations rise.

The commonly used warming projections – those highlighted in Intergovernmental Panel on Climate Change (IPCC) assessment reports – include a single best-estimate of carbon-cycle feedbacks. But they do not account for the large uncertainties in these estimates.

These uncertainties are “one of the dominant sources” of divergence between different model projections, according to Dr Ben Booth and colleagues at the Met Office Hadley Centre.

Climate campaigners, such as Greta Thunberg, have also expressed concern that climate projections typically do not fully incorporate the potential range of carbon-cycle feedbacks.

This article explores the implications of carbon-cycle feedback uncertainties by examining a number of modelling studies conducted by scientists over the past decade. These studies give a similar central estimate of carbon-cycle feedbacks to those used in IPCC projections.

But, at the high end, the results show these feedbacks could push atmospheric concentrations of greenhouse gases much higher – meaning more warming – from the same level of emissions.

Analysis for this article shows that feedbacks could result in up to 25% more warming than in the main IPCC projections.

…click on the above link to read the rest of the article…

Factcheck: Climate models have not ‘exaggerated’ global warming

September 22, 2017

Factcheck: Climate models have not ‘exaggerated’ global warming

A new study published in the Nature Geosciences journal this week by largely UK-based climate scientists has led to claims in the media that climate models are “wrong” and have significantly overestimated the observed warming of the planet.

Here Carbon Brief shows why such claims are a misrepresentation of the paper’s main results. In reality, the results obtained from the type of model-observation comparisons performed in the paper depend greatly on the dataset and model outputs used by the authors.

Much of the media coverage surrounding the paper, Millar et al, has focused on the idea that climate models are overestimating observed temperatures by around 0.3C, or nearly 33% of the observed warming since the late 1800s. For example, the Daily Mailreported:

According to these models, temperatures across the world should now be at least 1.3 degrees above the mid-19th century average, which is taken as a base level in such calculations. But the British report demonstrates that the rise is only between 0.9 and 1 degree.

Lead author Dr Richard Millar and his co-authors have pushed back against such media coverage, releasing a statement which says:

A number of media reports have asserted that our [study] indicates that global temperatures are not rising as fast as predicted by the Intergovernmental Panel on Climate Change (IPCC), and hence that action to reduce greenhouse gas emissions is no longer urgent. Both assertions are false. Our results are entirely in line with the IPCC’s 2013 prediction that temperatures in the 2020s would be 0.9-1.3 degrees above pre-industrial [levels].

[Carbon Brief’s guest post by Dr Millar earlier this week includes the paper’s key figures. Additionally, one of his co-authors, Prof Piers Forster, provides further reaction at the end of this article.]

Contrary to media claims, the study found that warming is consistent with the range of IPCC models, albeit a bit lower than the average of all the models.

…click on the above link to read the rest of the article…

Anthropocene climate, part two: Four degrees of devastation

September 17, 2015

Anthropocene climate, part two: Four degrees of devastation

If greenhouse gas emissions aren’t stopped soon, unprecedented and deadly heat waves will become the new normal in most of the world

Part one of this article discussed James Hansen’s demonstration that a relatively small increase in global average temperature – under 1°C – has already produced a significant increase in the frequency and intensity of extremely hot weather. Heat waves that were very rare in 1951-1980 became ten times more likely in 1981-2010. As one of Hansen’s associates pointed out, this was not speculation about a possible future, but actual experience: “this is not based on models or predictions, just on a straightforward statistical analysis of measured temperature data.”[1]

Other studies, using other methods, have come to the same conclusion.

A 2012 paper examined the “exceptionally large number of record-breaking and destructive heatwaves” in the first decade of this century. The authors found that, “many lines of evidence – statistical analysis of observed data, climate modelling and physical reasoning – strongly indicate that some types of extreme event, most notably heatwaves and precipitation extremes, will greatly increase in a warming climate and have already done so…. The evidence is strong that anthropogenic, unprecedented heat and rainfall extremes are here – and are causing intense human suffering.”[2]

A study of extreme weather events between 1997 and 2012 concluded that “the available evidence suggests that the most ‘extreme’ extremes show the greatest change. This is particularly relevant for climate change impacts, as changes in the warmest temperature extremes over land are of the most relevance to human health, agriculture, ecosystems and infrastructure.”[3]

Others have found that global warming made the 2012-2014 California drought significantly worse than it would have otherwise been, and that in Australia, where hot and cold records used to be set in about equal numbers, all-time hot weather records now outnumber cold records by 12 to 1.[4]

…click on the above link to read the rest of the article…

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