Introduction
This document offers science-based principles to guide implementation of natural climate solutions (NCS) at national and sub-national scales. These principles broadly support the inclusion of NCS among measures needed to meet targets associated with the Paris Climate Agreement that establishes a global framework to limit warming to less than 2°C.

NCS employ “negative emissions,” or GHGs removed from the atmosphere, and have a significant role to play in limiting warming along with emissions reductions. Land, inland waters, and coastal ecosystems currently remove about 30% of global annual carbon dioxide emissions, and have the potential to continue or even increase this critical carbon sequestration function—they could potentially deliver up to one-third of net emission reductions needed to remain within a 1.5- or 2-degree Celsius warming pathway by 2030 (Adams et al. 2021). Solutions that abate emissions using NCS are also estimated to be highly cost-effective when compared to engineered solutions, such as carbon capture, utilization, and storage (Griscom et al. 2020). Many forms of NCS are available to deploy immediately, at scale, without technological breakthroughs.

An advantage of NCS is that if carefully designed, the activities can have substantial co-benefits such as conserving biodiversity and protecting water supplies. However, realizing this potential will require careful analysis of options for deploying NCS, as well as monitoring of results which may be impacted by climate change.

The following principles are intended to help avoid specific unintended consequences of NCS implementation. Although the principles were developed with U.S. policies and programs in mind, the scope is not limited to U.S. borders, particularly considering that agricultural and forest products are internationally traded commodities, and that protecting biodiversity and reducing greenhouse gasses are globally recognized priorities.

The framework underlying these principles includes considerations of the time, space, and human dimensions:

• The time dimension recognizes that NCS involve changes in ecosystems and ecosystem management that have impacts spanning decades to centuries. The effectiveness of a particular climate solution will vary over these timeframes—some will be effective in the short term, and some in the long term—as the climate changes and other factors evolve. The expected benefits as well as co-benefits need to be evaluated both now and in the future.

• The spatial dimension reflects the fact that ecosystems are highly variable geographically, as are the various factors that influence ecosystems. For example, natural disturbances such as fire are much more common and severe in areas where drought and high temperatures are prevalent. Management practices also differ considerably by region, with some regions dominated by agriculture, some by silviculture, and some by protection from human-caused disturbances. Potential solutions will be different for these categories, as will the effectiveness of each solution for reducing greenhouse gas emissions to the atmosphere.

• The human or community dimension is critical because NCS will be implemented by people within specific social and economic contexts. All solutions have consequences that go beyond the goal of reducing greenhouse gasses, and people will be affected in different ways. Impacts may be positive, such as providing jobs and temperature regulation by planting trees in urban environments, or negative, impacting specific economic sectors such as agriculture and the forest products industry. Therefore, it is essential to evaluate how the different NCS will affect different communities, over different time frames, and in different regions.