# co2\_hi

The 1st point on the radiation use efficiency curve is comprised of the ambient CO2 concentration, 330 μL CO2/L air, and the biomass-energy ratio reported for [bm\_e](https://swatplus.gitbook.io/io-docs/introduction-1/databases/plants.plt/untitled-17).

In order to assess the impact of climate change on agricultural productivity, SWAT+ incorporates equations that adjust RUE for elevated atmospheric CO2 concentrations. Values must be entered for *co2\_hi* and [bm\_e\_hi](https://swatplus.gitbook.io/io-docs/introduction-1/databases/plants.plt/bm_e_hi) in the plant database whether or not the user plans to simulate climate change.

{% hint style="info" %}
For simulations in which elevated CO2 levels are not modeled, *co2\_hi* should be set to some number greater than 330 ppmv and [bm\_e\_hi](https://swatplus.gitbook.io/io-docs/introduction-1/databases/plants.plt/bm_e_hi) should be set to some number greater than [bm\_e](https://swatplus.gitbook.io/io-docs/introduction-1/databases/plants.plt/untitled-17).
{% endhint %}

To obtain radiation-use efficiency values at elevated CO2 levels for plant species not currently in the database, plants should be established in growth chambers set up in the field or laboratory where CO2 levels can be controlled. RUE values are determined using the same methodology described in the explanation of [bm\_e](https://swatplus.gitbook.io/io-docs/introduction-1/databases/plants.plt/untitled-17).


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://swatplus.gitbook.io/io-docs/introduction-1/databases/plants.plt/co2_hi.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.