What is Enhanced Rock Weathering (ERW)?

Dec 31

General information and resources to help you learn more about ERW

by: Jonathan Lambert on June 11, 2026

Welcome! You may have found your way here from the factsheet at our urban enhanced rock weathering (ERW) site at the NYU Urban Farm Lab. This introductory blog will slightly expand on each section of the factsheet to give you more details and resources. We will post new blog entries that continue to bring you along the project with us and answer questions such as:

Why urban ERW in NYC?
How exactly are we conducting (and monitoring) ERW?
Who is the team?
What do initial results look like?
What are opportunities for community involvement and citizen science?
And more…

The basics of ERW

ERW is one of many carbon dioxide removal (CDR) strategies that can be used to mitigate climate change. It specifically involves spreading crushed silicate rocks (referred to as feedstocks) over large areas in order to speed up the natural rock weathering process which removes CO₂ from the atmosphere. These rocks are volcanic in origin and are commonly found on islands like Iceland and Hawaii, however they are also readily-available in many other places globally. Overall, ERW has the potential to remove 0.5-2 gigatonnes of CO₂ from the atmosphere per year (up to 5% of yearly human carbon dioxide emissions). While CDR strategies like this were once seen as a last resort, to keep global warming below the established 1.5°C goal, they are now recommended by the Intergovernmental Panel on Climate Change. Therefore, CDR needs to scale fast, but we are still learning how to best implement strategies such as ERW, how to monitor their effectiveness, and how to assess their continued environmental and social impacts. Our “urban ERW” site in Greenwich Village will help push all of these research areas forward.

What is the science behind ERW?

As previously mentioned, ERW removes CO2 from the atmosphere by accelerating natural rock weathering. This acceleration is primarily a result of the increased surface area that comes with crushing rocks to sand-sized particles and spreading them over large surface areas. On geologic timescales (millions of years), weathering on large areas of silicate rock (such as tropical volcanic islands) has led to CO₂ drawdown from the atmosphere and has periodically cooled the planet. This occurs as atmospheric CO₂ which is dissolved in raindrops interacts with these rocks and the dissolved CO2 is converted into another form of carbon – bicarbonate ions (HCO3-). These ions are eventually transported to the ocean and locked away from the atmosphere for thousands to millions of years.

Our choice of location

ERW is most commonly conducted on agricultural fields. One reason for this is that the large swaths of land devoted to agriculture globally provide ample surface area to spread rocks on. However, another specific benefit of conducting ERW on croplands is that the infrastructure is already in place to spread large amounts of soil amendments and even rock. Many farms have been spreading limestone (referred to as “liming”) for centuries to reduce soil acidity (raise soil pH), and the feedstocks used for ERW can also be used to manage soil pH. In addition to climate benefits and soil pH management, ERW also has the potential to provide micronutrient fertilizer benefits.

Despite this preference for agricultural implementation, ERW has also been implemented on coastlines, occurs naturally on green clay tennis courts, and has potential to be employed on green roofs, in grasslands, and even on golf courses. We have chosen our site at the Urban Farm Lab because 1) ERW is most well-understood in agricultural environments, but also because 2) the site provides a unique opportunity to engage urban communities in discussions and citizen science around agriculture and climate solutions. These communities are often less exposed to these topics, and we expand on our goals for engagement and the logic behind our location-specific project design in the next blog piece.

Is ERW safe?

In addition to generating climate-benefiting bicarbonate ions when they weather, the feedstocks used for ERW (mainly basalt rocks and sometimes “ultramafic” rocks like peridotite) release elements such as Mg, Ca, Ni, Na, K, Fe, Al, and more. Some of these elements are beneficial to agriculture, as they are much needed plant micronutrients. However, at high concentrations some elements (such as Ni and Cr) can cause concern. This risk is highest when: 1) using large amounts of feedstock (such as over 50 tons per hectare), 2) deploying on acidic soils, and 3) using ultramafic feedstocks. We therefore avoid all 3 of these risk factors.

At your site, we have deployed 10 pounds of feedstock (the equivalent of 20 metric tons per hectare). We also use a very well-understood “blue ridge metabasalt” feedstock that has low concentrations of potentially toxic elements. And finally, the soils at the Urban Farm Lab at time of deployment averaged ~7.1 pH, which is on the basic/alkaline side of neutral (not acidic).

Our understanding of elemental release from ERW is rapidly growing thanks to recent studies on trace element accumulation and uncertainties of ERW. The urban ERW project lead (Jonathan Lambert) is also an active researcher in this field. He contributed to development of the ERW Metal Accumulation Calculator and is currently collaborating with nonprofit researchers at Cascade Climate to publish a comprehensive study of metal accumulation risk from ERW in agricultural soils.

Additional resources

If you would like to dive deeper into ERW, we have curated a (non-exhaustive) list of useful resources below from universities, researchers, nonprofits, and private industry stakeholders: