At present, NPO climate action literature has delved into different aspects of non-state climate action and has presented several valuable findings. In a literature review conducted by Kagan and Dodge (2022), they have determined several mechanisms based on the organisations’ efforts: (1) public policy advocacy; (2) advocacy for behaviour change; (3) participation in governance; (4) direct interventions, where TSOs might independently influence climate mitigation or adaptation. Public policy advocacy mechanism constitutes as 57% majority of the literature and it involves non-profit organisations influencing public policy at various levels, including international, national, and subnational levels. Framing, policy advocacy, and policy diffusion strategies are among the few utilised to impact climate policies. The next mechanism, advocacy for behaviour change, involves directly appealing to corporations and the public to change their behaviours towards climate change. This includes initiatives to promote carbon reduction at individual and household levels, as well as engagement with corporations to influence their corporate social responsibility practices. Next, the participation (of organisations) in governance mechanisms functions when these organisations participate in governance structures and processes related to climate change. Such activities include monitoring corporations, providing expertise, managing specific projects, and participating in regional collaborative arrangements. Lastly, the direct intervention mechanism operates when organisations are engaged in direct actions to further climate mitigation and adaptation efforts which includes managing conservation easements, deploying specific technologies like solar geoengineering, providing direct aid to climate-vulnerable populations, and implementing local energy programs.

Another literature review conducted by Hale et. al. (2020) found that there was an overwhelming focus on mitigation with a 95% majority of studies assessing the potential or past impact of non-state climate action on greenhouse gas (GHG) reduction, thus overlooking the potential of adaptation climate actions. Next, about 61% of the studies focused on the potential impacts rather than the impacts that they have achieved, which consisted of 9% of the studies that was assessed. Similarly, the emphasis was largely placed on the ambition and implementation by the non-state actors such as their targets and outputs, reducing the emphasis on the progress that they have made. Lastly, the review also found that there was a lack of estimation of indirect and interactive impacts resulting from their primary climate action when there could be spillover/causal effects that influences other actors to adopt similar strategies.

While NPO climate action literature has increasingly provided and gleaned several insights into this sector, it is mostly focused and based on western states and several other Asian countries. This leaves a research gap in terms of representation for other regions of the world where NPOs also exist and function. Such an imbalance creates at least two mutually-reinforcing barriers to the further advancement of the nonprofit literature: (1) an incomplete understanding of the wide-ranging diversity and complexities of the nonprofit and voluntary sector on a global scale; and (2) uncertainties regarding the external validity of existing nonprofit theories and empirical work beyond their original contexts.

Given the existing research gaps in non-profit and voluntary sector literature, there are several highlights in which future research can delve into to provide more comprehensive insights. Firstly, to accurately assess the long term impacts of these organisations’ efforts, future research such as longitudinal studies could shed light on the sustained effectiveness of TSO efforts over time and thus focus on the long-term impact of interventions in climate change mitigation and adaptation strategies. Secondly, most studies also often focused on interim outcomes rather than direct climate and community impacts. Thus, more research is needed to assess whether non-state organisation efforts result in actual climate change mitigation and adaptation outcomes. More research can be conducted on the role and effectiveness of NPOs in the global south to provide further valuable insights into how these organisations contribute to climate change mitigation and adaptation efforts in different socio-economic contexts. Across several literature reviews, climate change adaptation research is more lacking compared to mitigation strategies especially in the premise of climate vulnerable communities. Future studies can investigate the capacity of NPOs in supporting community adaptation efforts.