Passatwolken sind klimarobuster als gedacht

Bild der Wissenschaft:

Passatwolken sind klimarobuster als gedacht

Weit ausgedehnte Quellwolken beschatten im Bereich der Passatwinde große Teile der Erdkugel. Da sie die Sonnenstrahlung reflektieren, mildern sie die Erderwärmung ab. Bisherige Klimamodelle sagten jedoch einen Teufelskreis voraus: Demnach sorge die globale Erwärmung dafür, dass sich die kühlenden Wolken schneller auflösen als bisher, was wiederum eine weitere Aufheizung antreibe. Erstmals haben Forscher diese Vorhersage nun empirisch untersucht – und haben positive Nachrichten: Ihre Beobachtungen und Berechnungen legen nahe, dass die Wolken auch bei wärmerem Klima bestehen bleiben und weiter dabei helfen können, die Erwärmung der Erde abzufedern.

Nördlich und südlich des Äquators, in der Passatwindzone, beschatten dichte Quellwolken rund 20 Prozent der Erdoberfläche. Da sie die Sonnenstrahlung reflektieren, tragen sie entscheidend dazu bei, die Erwärmung der Erde abzumildern. Bisherige Klimamodelle gingen jedoch davon aus, dass die Wolken diese Funktion schon bald nicht mehr wahrnehmen könnten. Die Hypothese: Durch die Klimaerwärmung verdunstet zwar mehr Wasser aus dem Meer und sorgt für eine höhere Luftfeuchtigkeit an der Unterseite der Wolken. Doch die Luftmassen oberhalb der Wolken bleiben sehr trocken. Da der große Feuchtigkeitsunterschied durch Durchmischung ausgeglichen wird, könnten die Wassertröpfchen schneller als bisher verdunsten, sodass sich die Wolken bereits nach kurzer Zeit auflösen müssten.

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Fioramonti et al. auf The Conversation:

Global population hits 8 billion, but per-capita consumption is still the main problem

The world population has just hit a new record: 8 billion. As is often the case, there are heated debates about the planet’s so-called “carrying capacity” – the total number of people who can live on Earth sustainably. Experts are generally divided into two camps. There are those who argue that we need to drastically reduce the human population to avoid ecological catastrophe. And then there are those who believe that technology will find smart solutions without any need to actively tackle the issue head-on.

Scientists have been debating such demographic issues at least since the 18th century, when Thomas Malthus published An Essay on the Principle of Population, arguably the first global treatise on the relationship between population growth and scarcity. A few decades later, however, the Industrial Revolution (which the British economist had failed to anticipate) ushered the world into an era of abundance, relegating Malthus’s grim predictions about the inevitability of scarcity to the margins of scientific debate.

In a bestselling book published in the late 1960s, The Population Bomb, Stanford professor Paul Ehrlich brought the topic back, advocating for immediate action to limit population growth on a finite planet. This recommendation was reiterated a few years later by the Club of Rome, an international network of scientists and industrialists. Its 1972 report The Limits to Growth aptly demonstrated the dynamic relationship between increasing consumption and the idea of “planetary boundaries” which cannot be crossed without risking severe environmental change.

It’s true that some technologies have made production more efficient (think of fertilisers), thus alleviating the impact of population growth on resource use. But there is little doubt that the human race has massively overstepped the planetary boundaries, presently exceeding the safe operating space in six domains out of nine (see graphic above).

A smaller population could still be more destructive

It is difficult to estimate just how many humans the planet can carry sustainably, however. This is often overlooked in policy debates, which generally deal with the issue rather simplistically, resting on the assumption that increasing living standards will lead to lower birth rates. Therefore, the argument goes, the global population will decline as soon as continents like Asia and Africa reach similar development levels as Europe and North America

The fallacy here is to assume that only technology and population matter. These days environmental scientists generally agree that the overall impact is also a function of affluence (the so-called I=PAT equation). This can easily generate a paradox. Countries continue increasing their living standards by pushing up per-capita consumption, thus resulting in smaller populations but much bigger ecological impacts.

Take China. Its population growth rates have gone down significantly from 2.8% in the 1970s to the first decline in absolute terms this year. But in that period its overall consumption levels have increased enormously, resulting in a much worse net impact. The same applies to India and most emerging and developing economies. If this trend continues, we may end up with a smaller global population but significantly more destructive effects on the planet.

Developing a ‘wellbeing economy’

The time has come to rethink our approach to affluence and develop different ways to improve living standards. In a new report to the Club of Rome titled Earth4All, we argue that countries (especially the most industrialised) should replace the pursuit of economic growth with broader measures of social and ecological wellbeing. This would result in a significant decrease in material consumption, while not undermining overall quality of life.

What might this involve in practice? Policies should encourage better work-life balance and gender equality, as women’s empowerment is a key determinant of population growth. They should also optimise energy use and efficiency because the most renewable energy is what we do not need to use. We also need regenerative practices and homegrown solutions to manufacturing and food production (roughly 30% of food globally is either lost or wasted due to overconsumption and aesthetic standards).

Such a “wellbeing economy” approach would help all countries (including the poorest) leapfrog to a different type of development, able to combine high quality of life with very limited impacts on the environment. It is the difference between an extractive, linear economy that turns resources into emissions and a regenerative, circular economy that produces no waste because the output of any process becomes the input for another one.

There is massive room for improvement. After all, most of our wellbeing does not depend on material consumption (above a minimum sufficient level) but on the quality of our social relations and the environment in which we live. Ultimately, living better and more equitably will help us find the right balance also in terms of global population, without the need to impose restrictions.


Coffield & Randerson auf The Conversation:

Satellites detect no real climate benefit from 10 years of forest carbon offsets in California

Many of the companies promising “net-zero” emissions to protect the climate are relying on vast swaths of forests and what are known as carbon offsets to meet that goal.

On paper, carbon offsets appear to balance out a company’s carbon emissions: The company pays to protect trees, which absorb carbon dioxide from the air. The company can then claim the absorbed carbon dioxide as an offset that reduces its net impact on the climate.

However, our new satellite analysis reveals what researchers have suspected for years: Forest offsets might not actually be doing much for the climate.

When we looked at satellite tracking of carbon levels and logging activity in California forests, we found that carbon isn’t increasing in the state’s 37 offset project sites any more than in other areas, and timber companies aren’t logging less than they did before.

The findings send a pretty grim message about efforts to control climate change, and they add to a growing list of concerns about forest offsets. Studies have already shown that projects are often overcredited at the beginning and might not last as long as expected. In this case we’re finding a bigger issue: a lack of real climate benefit over the 10 years of the program so far.

But we also see ways to fix the problem.

How forest carbon offsets work

Forest carbon offsets work like this: Trees capture carbon dioxide from the air and use it to build mass, effectively locking the carbon away in their wood for the life of the tree.

In California, landowners can receive carbon credits for keeping carbon stocks above a minimum required “baseline” level. Third-party verifiers help the landowners take inventory by manually measuring a sample of trees. So far, this process has only involved measuring carbon levels relative to baseline and has not leveraged the emerging satellite technologies that we explored.

Forest owners can then sell the carbon credits to private companies, with the idea that they have protected trees that would otherwise be cut down. These include large oil and gas companies that use offsets to meet up to 8% of their state-mandated reductions in emissions.

Forest offsets and other “natural climate solutions” have received a great deal of attention from companiesgovernments and nonprofits, including during the U.N. climate conference in November 2022. California has one of the world’s largest carbon offset programs, with tens of millions of dollars flowing through offset projects, and is often a model for other countries that are planning new offset programs.

It’s clear that offsets are playing a large and growing role in climate policy, from the individual to the international level. In our view, they need to be backed by the best available science.

3 potential problems

Our study used satellite data to track carbon levelstree harvesting rates and tree species in forest offset projects compared with other similar forests in California.

Satellites offer a more complete record than on-the-ground reports collected at offset projects. That allowed us to assess all of California since 1986.

From this broad view, we identified three problems indicating a lack of climate benefit:

  1. Carbon isn’t being added to these projects faster than before the projects began or faster than in non-offset areas.
  2. Many of the projects are owned and operated by large timber companies, which manage to meet requirements for offset credits by keeping carbon above the minimum baseline level. However, these lands have been heavily harvested and continue to be harvested.
  3. In some regions, projects are being put on lands with lower-value tree species that aren’t at risk from logging. For example, at one large timber company in the redwood forests of northwestern California, the offset project is only 4% redwood, compared with 25% redwood on the rest of the company’s property. Instead, the offset project’s area is overgrown with tanoak, which is not marketable timber and doesn’t need to be protected from logging.

How California can fix its offset program

Our research points to a set of recommendations for California to improve its offsets protocols.

One recommendation is to begin using satellite data to monitor forests and confirm that they are indeed being managed to protect or store more carbon. For example, it could help foresters create more realistic baselines to compare offsets against. Publicly available satellite data is improving and can help make carbon offsetting more transparent and reliable.

California can also avoid putting offset projects on lands that are already being conserved. We found several projects owned by conservation groups on land that already had low harvest rates.

Additionally, California could improve its offset contract protocols to make sure landowners can’t withdraw from an offset program in the future and cut down those trees. Currently there is a penalty for doing so, but it might not be high enough. Landowners may be able to begin a project, receive a huge profit from the initial credits, cut down the trees in 20 to 30 years, pay back their credits plus penalty, and still come out ahead if inflation exceeds the liability.

Ironically, while intended to help mitigate climate change, forest offsets are also vulnerable to it – particularly in wildfire-prone California. Research suggests that California is hugely underestimating the climate risks to forest offset projects in the state.

The state protocol requires only 2% or 4% of carbon credits be set aside in an insurance pool against wildfires, even though multiple projects have been damaged by recent fires. When wildfires occur, the lost carbon can be accounted for by the insurance pool. However, the pool may soon be depleted as yearly burned area increases in a warming climate. The insurance pool must be large enough to cover the worsening droughts, wildfires and disease and beetle infestations.

Considering our findings around the challenges of forest carbon offsets, focusing on other options, such as investing in solar and electrification projects in low-income urban areas, may provide more cost-effective, reliable and just outcomes.

Without improvements to the current system, we may be underestimating our net emissions, contributing to the profits of large emitters and landowners and distracting from the real solutions of transitioning to a clean-energy economy.