Measuring greenhouse gas emissions from ponds improves climate predictions

Shallow lakes and ponds might seem innocuous in our landscape, but they have been found to emit substantial volumes of greenhouse gases into the atmosphere. Our understanding of the emissions from these water bodies, however, has been muddled due to significant variations in their emissions.

A recently conducted study led by Cornell University offers fresh insights into this issue. This study aimed to quantify methane and carbon dioxide emissions from 30 small lakes and ponds, each less than an acre in size. These bodies of water were situated in temperate regions across Europe and North America. Intriguingly, the team found that it was the smallest and shallowest of these bodies of water that demonstrated the greatest emission variability over time.

“These small and shallow bodies of water, though often overlooked, are now gaining prominence in the larger climate change narrative,” said study senior author Professor Meredith Holgerson.

The findings of this research have critical implications for the calibration of climate models. “The paper points to patterns across a broad geographic range, such that we can actually get in and predict which water bodies are going to vary and will be most variable,” noted Nicholas Ray, a postdoctoral researcher in Holgerson’s lab. Furthermore, the study underscores the urgent need to study these smaller bodies of water more meticulously.

Earlier research led by Holgerson’s team suggested that these shallow lakes and ponds could contribute about five percent of global methane emissions to the atmosphere. However, without precise measurements from a multitude of water bodies, the actual contribution could fluctuate between half to twice this figure.

Understanding the emission dynamics from these water bodies is crucial since both carbon dioxide and methane act as greenhouse gases. Notably, methane is 25 times more effective than carbon dioxide at trapping heat in our atmosphere.

For the study, each water body was sampled three times during the summers of 2018 and 2019. Sampling was done at three different locations, including the deepest point and two spots on opposite ends, while ensuring that these were not too close to the shoreline.

Ray revealed a key finding that “the smaller the system is, in regard to surface area, the higher emissions are likely to be.” For carbon dioxide, the samples were consistent across the entire water body. This indicated that just one sample could accurately predict the carbon dioxide emissions for the whole body of water. However, for methane, multiple samples from different locations were required to measure emissions accurately.

Additionally, the variability in carbon dioxide emissions seemed to be influenced heavily by the amount of plant life in the water. Meanwhile, the variability in methane emissions was more driven by the water depth, which could be linked to stratification in the water column.

Among other applications, this study paves the way for building more ponds as a part of New York State’s climate mitigation strategy. These ponds could also aid farmers in better managing droughts.

“We’re working to identify how ponds can be built, or if there are simple management strategies people can employ, to minimize emissions,” Ray said, revealing the proactive approach taken to utilize this new information.

More about climate models

Creating climate models is an intricate and fascinating process. These models are computer programs that simulate the interactions of the atmosphere, oceans, land surface, and ice. They are used by scientists to better understand the Earth’s climate and how it might change in the future.

Climate models work by dividing the planet into a 3D grid, which can focus on a specific area or cover the globe. Each grid box, and the layers above and below it, represents a chunk of the atmosphere, ocean, or land. 

The model then solves equations that describe the fluid motion and thermodynamics of the atmosphere and oceans, the transmission of sunlight through the atmosphere and oceans, the exchange of heat with the land and ice surface, and many other physical processes.

Types of climate models

There are several types of climate models, each serving a different purpose. For instance, simple climate models can be used to look at the Earth’s energy balance. These models can give a broad-brush view of the climate system and are useful for providing a rough idea of how changes in the Earth’s energy budget can affect global temperatures.

At the other end of the scale are complex climate models, also known as general circulation models (GCMs). These split the atmosphere, oceans, and land into many layers and boxes, allowing for the detailed study of individual climate processes and their interactions.

Some GCMs include a detailed representation of the carbon cycle, atmospheric chemistry, ice flow dynamics, and vegetation dynamics, which make them coupled climate-carbon-chemistry models. These models can investigate not just how climate change influences the carbon cycle and other biogeochemical cycles, but also how feedbacks from these cycles may impact the climate system.

Improving accuracy by incorporating more data

These models have become increasingly sophisticated, even incorporating elements such as cloud formation, vegetation cover changes, and the impact of volcanic emissions. However, climate models are not perfect and have limitations. 

For instance, there are uncertainties around how to accurately represent processes like cloud formation and precipitation at the scale of a grid box, and how to represent the indirect effects of aerosols.

Nevertheless, despite their limitations, climate models are essential tools for scientists, providing our best means of projecting future climate change scenarios based on different greenhouse gas emission pathways.

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