Before Human-Made Climate Change, Was Earth Actually in a Cooling Phase?

ENVIRONMENT19 February 2023

ByELLIE BROADMAN & DARRELL KAUFMAN, THE CONVERSATION

(StockByM/Getty Images)

Over the past century, the Earth's average temperature has swiftly increased by about 1 degree Celsius (1.8 degrees Fahrenheit). The evidence is hard to dispute. It comes from thermometers and other sensors around the world.

But what about the thousands of years before the Industrial Revolution, before thermometers, and before humans warmed the climate by releasing heat-trapping carbon dioxide from fossil fuels?

Back then, was Earth's temperature warming or cooling?

Even though scientists know more about the most recent 6,000 years than any other multi millennial interval, studies on this long-term global temperature trend have come to contrasting conclusions.

To try to resolve the difference, we conducted a comprehensive, global-scale assessment of the existing evidence, including both natural archives, like tree rings and seafloor sediments, and climate models.

Our results, published 15 February 2023, suggest ways to improve climate forecasting to avoid missing some important slow-moving, naturally occurring climate feedbacks.

Global warming in context

Scientists like us who study past climate, or paleoclimate, look for temperature data from far back in time, long before thermometers and satellites.

We have two options: We can find information about past climate stored in natural archives, or we can simulate the past using climate models.

Ellie Broadman, right, an author of this article, holds a sediment core from a lake on Alaska's Kenai Peninsula. 

(Emily Stone)

There are several natural archives that record changes in the climate over time. The growth rings that form each year in trees, stalagmites, and corals can be used to reconstruct past temperature.

Similar data can be found in glacier ice and in tiny shells found in the sediment that builds up over time at the bottom of the ocean or lakes. These serve as substitutes, or proxies, for thermometer-based measurements.

For example, changes in the width of tree rings can record temperature fluctuations. If the temperature during the growing season is too cold, the tree ring forming that year is thinner than one from a year with warmer temperatures.

Another temperature proxy is found in seafloor sediment, in the remains of tiny ocean-dwelling creatures called foraminifera. When a foraminifera is alive, the chemical composition of its shell changes depending on the temperature of the ocean.

When it dies, the shell sinks and gets buried by other debris over time, forming layers of sediment at the ocean floor. Paleoclimatologists can then extract sediment cores and chemically analyze the shells in those layers to determine their composition and age, sometimes going back millennia.

Climate models, our other tool for exploring past environments, are mathematical representations of Earth's climate system. They model relationships among the atmosphere, biosphere, and hydrosphere to create our best replica of reality.

Climate models are used to study current conditions, forecast changes in the future, and reconstruct the past.

For example, scientists can input the past concentrations of greenhouse gasses, which we know from information stored in tiny bubbles in ancient ice, and the model can use that information to simulate past temperature. Modern climate data and details from natural archives are used to test their accuracy.

Proxy data and climate models have different strengths.

Proxies are tangible and measurable, and they often have a well-understood response to temperature. However, they are not evenly distributed around the world or through time. This makes it difficult to reconstruct global, continuous temperatures.

In contrast, climate models are continuous in space and time, but while they are often very skillful, they will never capture every detail of the climate system.

A paleo-temperature conundrum

In our new review paper, we assessed climate theory, proxy data, and model simulations, focusing on indicators of global temperature.

We carefully considered naturally occurring processes that affect the climate, including long-term variations in Earth's orbit around the Sun, greenhouse gas concentrations, volcanic eruptions, and the strength of the Sun's heat energy.

We also examined important climate feedbacks, such as vegetation and sea ice changes, that can influence global temperature.

For example, there is strong evidence that less Arctic sea ice and more vegetation cover existed during a period around 6,000 years ago than in the 19th century. That would have darkened the Earth's surface, causing it to absorb more heat.

Our two types of evidence offer different answers regarding the Earth's temperature trend over the 6,000 years before modern global warming.

Natural archives generally show that Earth's average temperature roughly 6,000 years ago was warmer by about 0.7 °C (1.3 °F) compared with the 19th century median, and then cooled gradually until the Industrial Revolution. We found that most evidence points to this result.

Meanwhile, climate models generally show a slight warming trend, corresponding to a gradual increase in carbon dioxide as agriculture-based societies developed during the millennia after ice sheets retreated in the Northern Hemisphere.

How to improve climate forecasts

Our assessment highlights some ways to improve climate forecasts.

For example, we found that models would be more powerful if they more fully represented certain climate feedbacks.

One climate model experiment that included increased vegetation cover in some regions 6,000 years ago was able to simulate the global temperature peak we see in proxy records, unlike most other model simulations, which don't include this expanded vegetation.

Understanding and better incorporating these and other feedbacks will be important as scientists continue to improve our ability to predict future changes.

Ellie Broadman, Postdoctoral Research Associate in Climate Science, University of Arizona and Darrell Kaufman, Professor of Earth and Environmental Sciences, Northern Arizona University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Puppies spontaneously imitate human actions

ByAndrei Ionescu

Earth.com staff writer

02-17-2023

A team of researchers from the Eötvös Loránd University (ELTE) in Hungary has recently investigated whether young puppies, wolf pups, and kittens have different tendencies to observe and imitate human actions, without pre-training or food or toy rewards. The experiments revealed that puppies – but not kittens or wolf cubs – tended to spontaneously imitate what humans did, even if they were not offered any rewards.

Imitating what others do in a new situation is an efficient way for individuals to learn about their environments and the possibilities it offers. Moreover, besides helping them learn new skills or new information, copying another’s actions is also a way of promoting belonging to a social group.

In their experiments, the researchers first observed how 42 puppies, 39 kittens, and eight wolf pups – all socialized and living in human families – reacted to a novel object placed in a room (such as touching it with their nose or paw). In a second step, while the owner was holding the pet, the experimenter demonstrated a different type of action on the object. For instance, if the animal previously touched the object with its nose, the experimenter touched it with her hand. Finally, the scientists observed whether the animals eventually performed the same action on the object.

“Since paying attention to the demonstration is a fundamental requisite for social learning, we first assessed whether the puppies, kittens, and wolf pups looked at us when we performed the demonstration,” explained study lead author Claudia Fugazza, an ethologist at ELTE. “While typically the puppies looked at us almost immediately, it took four-five times longer to get the attention of wolf pups and kittens.”

Although both puppies and wolf pups replicated the demonstrated actions in nearly 70 percent of the trials (twice as often as kittens), only puppies tended to imitate the actions with a body part homologue to that of the human experimenters, even if the action differed from the action they performed before watching a demonstration.

“Typically, most subjects touched the object with their nose, when they had not observed a demonstration. However, after observing the experimenter touching the object with her hand, the puppies tended to touch it using their paw,” reported study co-author Stefania Uccheddu, another ethologist from the same university.

These findings could be explained by the fact that while dogs’ and wolves’ ancestors were social animals with intense within-group collaboration for survival, cats’ ancestors were solitary hunters. In addition, dogs were domesticated much earlier than cats (between 20,000 and 40,000 versus 10,000 years ago) and were selected for various forms of collaboration with humans. By contrast, cats had a different domestication process: although they hunted mice, rats, or snakes in the human environment, they did not have to closely cooperate or communicate with human

“We believe that our findings can form the basis for the development of novel training methods that rely on the tendency of puppies to learn by observation and to imitate human actions. This way, dog training can be less dependent on the use of food rewards and more able to take advantage of dogs’ natural propensity for social learning,” concluded senior author Ákos Pogány, an assistant professor of Biology at ELTE.

The study is published in the journal Nature Scientific Reports.

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By Andrei Ionescu, Earth.com Staff Writer

Plants are responding much faster to climate change than expected

ByCalum Vaughan

Earth.com staff writer

02-17-2023

When people think about the negative impacts of climate change, they normally think of species and plants becoming completely extinct, and whilst this is a huge problem, many plants are able to adapt their to warming temperatures. Whilst these shifts in behaviors are signs that a species is struggling to survive, they can also help to provide researchers with insights into the velocity of climate change as well as aid conservation planning. 

A new study from Brown University in Providence, Rhode Island has explored exactly this concept, studying the vegetation cover across mountainous western North America and the way species are adapting to climate change. Study lead author James R. Keller and colleagues hypothesized that species were shifting their distribution north to higher elevations in order to recover their natural temperature range. 

This adaptive ability has not been well documented, but in an effort to better understand it, the researchers analyzed 27 years’ worth of high-resolution satellite elevation data from between 1984 and 2011 within nine North American mountain ranges. Based on the images, the experts were able to quantify vegetation cover changes at different altitudes across a wide range of tropical, subarctic, coastal, and desert ecosystems. 

The data clearly showed that across all studied ecosystems, upward shifts of vegetation toward higher elevations were ubiquitous, and occurred at rapid velocities. These velocities were identified to be significantly faster than the responses of animals to warming temperatures. 

However, further research will be needed to consider more recent data, as the satellite data collected did not include imaging from the last twelve years. Furthermore, the lack of data prior to 1984 makes it less certain for the researchers to confirm that vegetation distribution truly has a direct correlation with climate change. 

“Our findings help to characterize patterns of vegetation across elevations in mountains that range from the subtropics to the subarctic. If substantiated, this finding could warrant reconsideration of a current cornerstone of conservation planning,” wrote the researchers.

“More work is needed to better contextualize how the vegetation shifts we observed, which measure any green vegetation, relate to individual species movements and broader ecosystem transitions–as this sort of integration offers the potential to create a more holistic understanding of change in montane systems”.

The authors concluded by expressing their gratitude for the modern satellite imaging data that we take for granted today: “NASA satellites, in combination with powerful computing, provide a view of our planet like never before, giving us the ability to understand how natural ecosystems are responding to changes in the environment.

The research findings have been published in the journal PLOS Climate.

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World Pangolin Day: project launched to save the elusive mammal

ByChrissy Sexton

02-18-2023

Earth.com staff writer

With funding from the Paul G. Allen Family Foundation, researchers and conservationists have launched Operation Pangolin in an effort to save endangered pangolins from extinction. 

The pangolin is the most trafficked wild mammal in the world, and is also among the least studied animals. This makes it difficult for experts to develop effective conservation strategies.

There are eight species of pangolins, all of which are protected under national and international laws. Even still, pangolins are illegally trafficked for sale of their scales.

Dr. Dan Challender is an interdisciplinary conservation scientist based in Oxford University’s Department of Biology and the Oxford Martin School who has been involved in pangolin research and conservation for 15 years. 

“In the last decade pangolin populations in Central Africa have been under increasing pressure from offtake for local use and international trafficking of their scales,” said Dr. Challender.

“This project has the potential to transform pangolin conservation, first in key locations in Central Africa, and then extending into parts of Asia. By taking an interdisciplinary approach and using novel technology and artificial intelligence methods, the project will give pangolin populations in these regions the best chance of survival.”

Matthew H. Shirley from Florida International University is the project lead for Operation Pangolin.“Without urgent conservation action at a global scale, all eight species of pangolins face extinction,” said Shirley. “Operation Pangolin is a chance to alter the conservation landscape for pangolins and other wildlife threatened by illicit human behavior.”

According to a press release, the team is developing toolkits for pangolin monitoring and data collection, a critical first step to prevent extinction of these evolutionarily distinct and imperiled mammals. 

“Accurate, actionable data is the foundation of effective conservation efforts,” said Gabe Miller, director of technology on behalf of the Paul G. Allen Family Foundation. “Operation Pangolin will provide a blueprint for how conservationists can turn data into solutions that address important issues like wildlife trafficking and the biodiversity crisis head on.”

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By Chrissy Sexton, Earth.com Editor