The Intergovernmental Panel on Climate Change, or IPCC, has been writing reports for years showing that global targets on CO2 emissions reductions will not be met without greater utilization of nuclear fission
Perhaps they did in the past -- I honestly don't know -- but they don't anymore (2022 summary). They mention nuclear as an option on pg 38, but it clearly has a lower cost/benefit than wind and solar.
On page 67 of the technical summary, they write
The political, economic, social, and technical feasibility of solar energy, wind energy and electricity storage technologies has improved dramatically over the past few years. In contrast, the adoption of nuclear energy and CO2 capture and storage (CCS) in the electricity sector has been slower than the growth rates anticipated in stabilisation scenarios. Emerging evidence since AR5 indicates that small-scale technologies (e.g., solar, batteries) tend to improve faster and be adopted more quickly than large-scale technologies (nuclear, CCS) (medium confidence). [emphasis mine]
Even in their 2019 report they propose nuclear *as an option*, but state:
Nuclear power increases its share in most 1.5 [degree] C pathways with no or limited overshoot by 2050, but in some pathways both the absolute capacity and share of power from nuclear generators decrease (Table 2.15). There are large differences in nuclear power between models and across pathways (Kim et al., 2014; Rogelj et al., 2018). One of the reasons for this variation is that the future deployment of nuclear can be constrained by societal preferences assumed in narratives underlying the pathways (Oâ(TM)Neill et al., 2017; van Vuuren et al., 2017b). Some 1.5ÂC pathways with no or limited overshoot no longer see a role for nuclear fission by the end of the century, while others project about 95 EJ yrâ'1 of nuclear power in 2100 (Figure 2.15).
In other words, nuclear is only one of many possible routes, and so only "necessary" absent the uptake of alternatives.
Scientific studies tell us that if we don't increase our utilization of nuclear fission power then we won't meet the CO2 emission reduction goals we set for ourselves.
Which studies? How recent are they, and how accurate are/were their estimates for the relative costs, efficiencies, and deployment timelines of various options? PV solar conversion efficiency has increased moderately over just the past decade, while cost-per-watt has plummeted by nearly a factor of 10. (Sources: https://www.nrel.gov/news/prog..., https://ourworldindata.org/gra..., https://www.irena.org/publicat...)
Meanwhile, nuclear only gets more expensive to build, operate, and decommission, and doesn't really benefit from economies of scale in any meaningful way, despite assumptions to the contrary. Time and budget estimates for commissioning new plants are notoriously conservative: Georgia's latest plant took 87% longer and cost 121% more than estimated, for example, and that's not even an extreme example of cost overruns, which have historically been as high as 1000%. In fact, it's well below the average of 240%. Presumed nth-of-a-kind vs. first-of-a-kind savings rarely materialize, and tend to be outweighed by site- and project-specific costs in any case. While that may not be a function of nuclear power itself, it does seem to be the reality for building plants. Long-term storage of nuclear waste is also problematic logistically, financially, politically, and ethically, Yes, it "should" be as simple as burying it deep underground, or reusing it in one of many possible ways, but the reality of accomplishing that brings to mind the "draw the rest of the fucking owl" meme.