Altcoin December Outlook: Dovish Tailwinds and Aerospace Gains Face Carbon Pressures

December has long been a pivotal period for cryptocurrency markets, with historical patterns suggesting a seasonal surge in altcoin activity. As 2025 approaches, investors are scrutinizing macroeconomic indicators to determine whether this year will mirror past trends. Recent data on Treasury yields, carbon pricing, and aerospace sector performance offer insights into the potential for a December altcoin rally, while highlighting key assets to monitor.

The U.S. 13-week Treasury bill (^IRX) has shown a gradual decline in yields since mid-October 2025, settling at 3.737% on November 26. This easing of borrowing costs aligns with broader Federal Reserve signals of a dovish pivot, which historically reduces pressure on risk assets. Lower yields often incentivize capital flows into high-volatility sectors like cryptocurrencies, as investors seek higher returns amid reduced opportunity costs. For altcoins, which typically outperform Bitcoin during bullish phases, this could signal favorable conditions for a December rally.

Meanwhile, the S&P 500 Aerospace & Defense sector has seen a 0.73% gain in its latest session on November 28, 2025. While not a direct indicator for crypto, the sector's performance reflects broader market risk appetite and investor confidence in capital expenditures. Aerospace stocks often benefit from macroeconomic stability and geopolitical calm-conditions that could also support speculative trading in altcoins. The sector's upward momentum suggests a market environment conducive to alternative asset classes.

Carbon pricing data from Platts further adds nuance. The Regional Greenhouse Gas Initiative (RGGI) and California Cap-and-Trade (CCA) allowances closed at $28.61 and $30.03 per allowance, respectively, on November 25, 2025. These increases, while modest, indicate tightening regulatory scrutiny on emissions-a trend that could indirectly impact energy-intensive crypto mining operations. However, the California Carbon Offset (CCO) price at $15.85 per metric ton suggests a more moderate regulatory stance, balancing potential cost pressures for miners.

For altcoin investors, the interplay of these factors creates a mixed but cautiously optimistic outlook. A dovish monetary policy environment and stable aerospace markets support risk-on behavior, while carbon pricing trends highlight regulatory tailwinds that could influence energy costs. Among altcoins, assets with strong institutional adoption, energy-efficient consensus mechanisms, or regulatory clarity are likely to outperform.