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Most investors have no idea how climate friendly their investment portfolios are. A portfolio built around S&P 500 index funds like SPY quietly holds ExxonMobil (XOM), Chevron (CVX), and other fossil fuel adjacent firms. To help investors steer clear from fossil fuels in their investment decisions, Ziggma measures the climate impact of every holding — and attributes a single, actionable climate score to every portfolio.
The energy sector represents only around 2.8% of S&P 500 index weight. That number is misleading. Despite their small weight, energy and utilities companies together account for approximately 70% of total greenhouse gas emissions across the entire index — a disproportion that makes fossil fuel exposure essentially impossible to avoid in a standard broad-market portfolio.
The Dow Jones Industrial Average has shed most of its fossil fuel exposure over the decades. Chevron (CVX) remains its sole oil-and-gas component. ExxonMobil (XOM) — which was removed from the Dow in 2020 — still sits in the S&P 500 with a market cap above $500 billion, making it one of the index's largest individual fossil fuel exposures.
The hidden layer goes further. Nearly 1 in 5 of the 500 largest US companies by market cap carries meaningful fossil fuel exposure — through reserves, refining operations, or fossil-fuel-dependent supply chains — according to screening data from As You Sow. Getting to a genuinely Paris-aligned portfolio requires removing or reducing all of them, not just the obvious names.
Global Warming Potential (GWP) is Ziggma's portfolio-level temperature metric. It translates the emissions trajectory of everything you own into a single number: the degree of warming the world would see if every company matched your portfolio's climate behavior. That 4.1°C figure is the S&P 500's GWP. Ziggma's GWP gauge makes the exposure visible holding by holding. It is the first step toward knowing where you actually stand.
Climate researchers use implied temperature rise as the benchmark. A portfolio financing a clean energy transition implies less warming than one holding coal and oil producers. The scale below shows how portfolios are typically classified.
Ziggma sources GWP data from ACA Ethos, a specialist impact data provider. Each holding gets an individual GWP score. Ziggma then weights those scores by your position size to produce a single portfolio-level reading.
A holding like NextEra Energy (NEE) scores 2.0°C. First Solar (FSLR) scores 1.3°C. SPYX — the State Street SPDR S&P 500 Fossil Free Reserves ETF — reduces overall portfolio GWP by excluding companies with proved fossil fuel reserves.
Ziggma GWP gauge — desktop and mobile. A reading of 2.28°C means this portfolio is financing warming above the 2°C threshold. Holdings like First Solar (FSLR) and NextEra Energy (NEE) pull the score down. SPYX pushes it lower still by excluding fossil fuel reserves entirely.
The problem is hidden fossil fuel exposure inside funds investors consider diversified or even responsible.
SPY and QQQ both hold ExxonMobil (XOM) and Chevron (CVX) by market weight. Most investors don't realize this. Even ESG-labeled funds can carry mixed-impact positions — Ziggma rates CCSO (Carbon Collective Climate Solutions U.S. Equity ETF) as "Mixed" in its Impact Analysis. iShares Global Clean Energy ETF (ICLN) scores better at 2.1°C but still sits above the 2°C threshold.
The median S&P 500 portfolio is currently tracking above 2.7°C. Getting below 2°C requires actively replacing high-GWP holdings — not just adding clean energy positions on top.
The Ziggma Portfolio Checkup flags your three lowest-impact holdings automatically. It shows each holding's GWP rating alongside its overall Impact Score so you can see exactly what's pulling your portfolio's climate score up.
Improving your portfolio's climate score means reducing high-GWP holdings — not just adding green ones on top.
Three approaches work for self-directed investors.
SPYX (State Street SPDR S&P 500 Fossil Free Reserves ETF) screens out companies with proved coal, oil, and gas reserves. This alone can reduce a broad-market portfolio's implied warming by 0.3°C–0.5°C.
Bloom Energy (BE) and First Solar (FSLR) both carry GWP scores below 2.0°C. iShares Global Clean Energy ETF (ICLN) offers diversified clean exposure at 2.1°C — still above 1.5°C but well below the broad market average.
Companies with published Science Based Targets initiative (SBTi) commitments are legally accountable for hitting interim milestones. Microsoft (MSFT) targets carbon negative by 2030. Apple (AAPL) targets net-zero across its entire supply chain by 2030. Amazon (AMZN) commits to net-zero carbon by 2040 under its own Climate Pledge. All three carry lower transition risk than peers without published targets.
Ziggma's Screener lets you filter holdings by GWP and impact score, surfacing lower-carbon alternatives before you run them through the Portfolio Optimizer.
Ziggma's GWP gauge gives every holding a climate score, weighted by your actual position sizes. The reading below is from a real portfolio. 2.28°C means it is financing warming above the 2°C threshold. The target is to get that number down.
The gauge appears inside the Impact tab of the Ziggma portfolio dashboard. It updates in real time as you add or remove holdings. Data comes from ACA Ethos.
