Joshua discusses the Advance Research for Climate Emergencies (ARC) Initiative at Renaissance Philanthropy, through which the team identifies experts and ideas, incubates them from small seed grants into fully staffed build-grant programs, and launches them.

Joshua traces his ambitious, technically rigorous approach to his years at DARPA, which gave him permission to chase ideas others called impossible. Widely sought out for mentorship, he talks about the Climate Emergency Forum and issues an appeal to scientists and nonprofit leaders.

*Tacit Knowledge *
Hosted by Kumar Garg
Presented by Renaissance Philanthropy
Subscribe to our Substack
Produced by All Together Now

FOLLOW JOSHUA

LinkedIn: https://www.linkedin.com/in/joshuawrightelliott/

Substack (The ARC): https://arcinit.substack.com/

KEY QUESTIONS & TAKEAWAYS

What is the "Sulfur Tracking Program" trying to figure out?

An in-development ARC initiative (still under a stealth name) aimed at launching small satellites and balloon-based sensors to resolve one of climate science's biggest open questions: how much of the Earth's declining reflectivity is due to falling aerosol pollution versus a warming-driven feedback loop that's itself reducing cloud cover.

Why might Earth's declining reflectivity be as big a driver of warming as greenhouse gases?

NASA's CERES satellite data suggests the planet has lost enough reflectivity since 2000 to contribute roughly 2.7 W/m² of climate forcing — a number comparable to the instantaneous forcing from all greenhouse gases emitted since the Industrial Revolution. That comparison is still being finalized in peer review, but it points to a second, under-discussed pillar of climate change alongside emissions.

Why has industrial pollution been masking warming, and what happens as it's cleaned up?

Burning fossil fuels releases sulfur dioxide and other aerosols that seed brighter, more reflective clouds. That pollution layer is estimated to be offsetting about half a degree of global warming — meaning, as Joshua puts it, we're already living in a "near two-degree world" that's been masked by the dirtiest possible form of accidental geoengineering. As pollution controls reduce aerosol emissions, that masking effect declines too.

What's driving the rest of the loss in Arctic ice and cloud cover?

About 30% of lost reflectivity comes from vanishing ice and snow cover (largely Arctic sea ice, mountain glaciers). The remaining majority comes from changes in cloud cover — and current observational and modeling capabilities can't yet disentangle how much of that is falling aerosol pollution versus a self-reinforcing, warming-induced feedback loop.

Why do the most accurate climate models predict more warming, not less?

A recent study comparing the ~40 global climate models in the CMIP archive found that the models which most accurately reproduce observed changes in reflectivity and Earth's energy imbalance also tend to show 1.5–2x higher climate sensitivity than the model average. If those more accurate models are right, a projected 2.5–3°C future could actually be closer to 4.5–5°C.

What is the Heilmeier Catechism, and how does Joshua use it?

A set of pressure-testing questions developed by former DARPA director George Heilmeier to evaluate research proposals. Joshua distills it into four core questions he uses as a first-pass filter for any ambitious idea: what are you trying to do, who's doing it now and what's wrong with that, what's your big insight, and who cares.

What are the ARC Initiative and BiTS?

ARC (Advanced Research for Climate Emergencies) is Renaissance Philanthropy's "nonprofit venture studio" model for finding experts and ideas and building them into fundable climate programs, incubating efforts like the Arctic Stabilization Initiative. BiTS (Big if True Science Accelerator) is a related program Joshua co-designed to teach scientists and engineers how to turn ambitious ideas into coordinated, fundable research programs — modeled on the DARPA program-manager playbook.

On program design and ambition

• Joshua credits his time at DARPA with giving him "permission" to think in 20–40 year horizons and pursue ideas most people call impossible — his rule of thumb is that if fewer than 30% of the people you talk to say your idea is impossible, you're not being ambitious enough.
• His approach to building expertise quickly is deliberately social: talking to 20 to 100 people in a dense stretch of time, using each conversation to get referred to others, rather than relying only on published research.
• His most recent program-design insight is about timing: bringing in a wide group of field experts (a "PI meeting" or workshop) only once there's a strong-enough shared mental model to make the conversation productive — citing the "forming, storming, norming, performing" framework for how new groups become effective, and the goal of minimizing time spent "storming."

Links:

• Joshua Elliott — Chief Scientist at Renaissance Philanthropy. Previously a Program Manager at DARPA's Information Innovation Office for six years, where he directed nearly $600M in federal R&D funding; before that, spent almost a decade in academia on computational climate economics and energy systems modeling at the University of Chicago and Argonne National Laboratory.
• Renaissance Philanthropy — The organization producing Tacit Knowledge Podcast, where Joshua leads climate and energy program development.
• ARC Initiative (Advanced Research for Climate Emergencies) — Renaissance Philanthropy's philanthropic fund and "nonprofit venture studio" for translational R&D on catastrophic climate risks — tipping points like ice sheet collapse, Arctic destabilization, and runaway methane emissions — which incubated the Arctic Stabilization Initiative.
• BiTS (Big if True Science Accelerator) — A 15-week accelerator co-designed and co-run by Joshua Elliott and JP Chretien (both former DARPA program managers) that teaches scientists and engineers how to turn ambitious ideas into fundable, coordinated research programs.
• NASA CERES (Clouds and the Earth's Radiant Energy System) — The NASA satellite mission, operating continuously since March 2000, that measures Earth's energy imbalance — the data source behind Joshua's reflectivity-loss figures.
• Heilmeier Catechism — A set of questions developed by former DARPA director George H. Heilmeier to pressure-test research proposals; DARPA's official version lists eight questions, though Joshua describes using a compressed four-question version of his own in practice.