Hawai’i, a tropical paradise known for its lush landscapes and rich biodiversity, is also prone to varying levels of rainfall throughout the year. While El Niño-Southern Oscillation (ENSO) has long been recognized as a significant driver of climate variability across the Pacific, new research reveals that another crucial climate pattern, the Pacific Meridional Mode (PMM), plays a vital role in shaping Hawai’i’s rainfall patterns.

Led by University of Hawai’i at Manoa atmospheric scientists, this groundbreaking study published in the Journal of Climate sheds light on the impact of PMM on spring rainfall, particularly for Maui and the Big Island. According to Dr. Pao-Shin Chu, co-author and Hawaii State Climatologist, “Our study suggests that although El Niño emerges as the primary driver of winter rainfall variability in Hawai’i, the Pacific Meridional Mode has a pivotal role in spring rainfall.”

The PMM operates in two distinct states: positive and negative. During the positive state, weaker trade winds prevail, accompanied by increased sea surface temperatures. Conversely, stronger trade winds and cooler surface temperatures are observed during the negative state.

Researchers Bo-Yi Lu and Dr. Chu employed diagnostic analyses using actual weather data, sea surface observations, and weather model-generated information to understand how these PMM patterns influence rainfall variations across Hawai’i.

Their findings indicate that a positive PMM state in spring leads to increased rainfall throughout the islands as cold fronts move through. This phenomenon is particularly pronounced on the windward sides of the islands, where the increased rainfall can exacerbate the risk of flooding. The leeward sides, however, tend to experience an increase in extreme rainfall events.

Interestingly, whether the positive PMM state occurs in winter or spring, the result is an elevated risk of floods on the leeward sides of the Hawaiian Islands. Conversely, a negative PMM state corresponds with reduced daily rainfall over windward sides, potentially worsening drought occurrences.

As Hawai’i’s population grows, so does the demand for water resources. This increased pressure underscores the need to comprehend the intricate relationship between rainfall and climate variability. As Dr. Chu emphasizes, “This uncertainty in interannual rainfall, together with the increasing demand for water, requires us to better understand the relationship between rainfall and climate variability.”

By shedding light on the pivotal role of PMM in Hawai’i’s rainfall patterns, this research aims to empower communities with climate and weather information, ultimately contributing to more informed decision-making for disaster preparedness and resource management.

Heat and Habitat: Bees Suffer from a Perfect Storm

The world is facing an unprecedented decline in insect numbers, with some studies suggesting that their biomass has almost halved since the 1970s. This alarming trend can be attributed to habitat loss due to agriculture, urbanization, and climate change. While these global change drivers have been well-documented, their interaction and impact on insects are not as well-known.

Researchers at Julius-Maximilians-Universität Würzburg (JMU) conducted a study at 179 locations throughout Bavaria, part of the LandKlif research cluster coordinated by Professor Ingolf Steffan-Dewenter within the Bavarian Climate Research Network bayklif. The results, published in Proceedings of the Royal Society B: Biological Sciences, reveal a complex and concerning relationship between heat, land use, and insect populations.

Bees are particularly affected

The study found that insects from different trophic levels react differently to the combination of higher temperatures and more intensive land use. Bees were particularly affected, with their numbers reduced by 65 percent in urban areas compared to forests. The researchers attribute this decline to not only hot daytime temperatures but also warmer than average nights.

Dr. Cristina Ganuza, a biologist involved in the study, highlights the significance of night-time temperatures: “Precisely because average night-time temperatures rise even faster than daytime temperatures.” This previously unknown effect on insects reveals a new threat that requires further research to uncover the underlying physiological mechanisms.

Key findings

The researchers summarize their findings in three key points:

1. Warmer daytime temperatures lead to higher numbers and diversity of bees, but only in forests and grasslands, the most natural habitats. Therefore, preserving and creating interconnected natural habitats within agricultural and urban areas is crucial.
2. Higher night temperatures lead to lower bee richness across all studied habitat types, highlighting a previously unknown negative effect on insects.
3. Climate change and land use interact, affecting insects at different trophic levels in distinct ways, which could disrupt food webs and important ecosystem functions like pest control and pollination.

The study emphasizes the importance of addressing climate change and land use to protect insect populations, particularly bees. By preserving natural habitats and creating interconnected areas within agricultural and urban landscapes, we can mitigate the negative impacts on these vital pollinators.

The study published in Nature Climate Change sheds light on the disproportionate impact of the world’s wealthiest individuals on global warming since 1990. According to the research, the top 10% of the global population is responsible for two-thirds of observed global warming and the resulting increases in climate extremes such as heatwaves and droughts.

The study assesses the contribution of high-emitting groups within societies, finding that the top 1% of the wealthiest individuals globally have a carbon footprint 26 times higher than the global average when it comes to monthly 1-in-100-year heat extremes. This also applies to Amazon droughts, with these emissions being 17 times more detrimental.

Lead author Sarah Schöngart explains, “Our study shows that extreme climate impacts are not just the result of abstract global emissions but can be directly linked to our lifestyle and investment choices, which in turn are linked to wealth.”

Using a novel modeling framework combining economic data and climate simulations, researchers were able to trace emissions from different global income groups. They found that emissions from the wealthiest 10% in the United States and China alone led to a two-to threefold increase in heat extremes across vulnerable regions.

The study’s findings are clear: if everyone had emitted like the bottom 50% of the global population, the world would have seen minimal additional warming since 1990. Coauthor Carl-Friedrich Schleussner emphasizes that addressing this imbalance is crucial for fair and effective climate action.

Moreover, the research highlights the importance of emissions embedded in financial investments rather than just personal consumption. Targeting the financial flows and portfolios of high-income individuals could yield substantial climate benefits.

“This is not an academic discussion – it’s about real impacts of the climate crisis today,” says Schleussner. “Climate action that doesn’t address outsize responsibilities of wealthiest members society risks missing one most powerful levers we have to reduce future harm.”

The authors suggest that their findings could motivate progressive policy instruments targeted at societal elites, noting such policies can foster social acceptance of climate action. Making rich individual polluters pay can also provide much-needed support for adaptation and loss and damage in vulnerable countries.

In conclusion, the study emphasizes the need to rebalance responsibility for climate action in line with actual emissions contributions is essential not just slow global warming but achieve more just resilient world.