Human records are also an important source of information for understanding past climates. What’s more, when climatologists and historians collaborate, they can open up a whole new field of research. For instance, historical maps and paintings can depict frozen rivers, glacier extent, and various plant species. Together, these sources paint a picture of what the climate was like in the past.

Humans as a climate witnesses:

While ice cores can provide insights into the climate of the last 800,000 years, historical data is limited to the period of human documentation. Nevertheless, it is important to gain a deeper understanding of the state of the Earth during our ancestors’ time. In Libya, for example, historians have found cave paintings of elephants, giraffes, and swimmers. These areas are deserts today, but the paintings show that the region wasn’t always so arid. A more humid climate favoring vegetation and water sources must have prevailed for people and animals to live there.

Figure 1: The deserts in northern Africa were once greener. Cave paintings from Libya often show animals that cannot survive there anymore.
Roberto D’Angelo (roberdan) – This image was originally posted to Flickr as DSCN3916

A study by Manning and Timpson (2014) supports this argument. The researchers analyzed over 1,000 bone, wood, charcoal, seed, and other plant and animal remains across the Sahara Desert. Using C14 analysis, they were able to date those findings. They located large clusters of human presence between 10,500 and 5,500 years before present (BP), indicating that the region was much more habitable at that time. This time span is known as the African Humid Period, when the Sahara was greener and had lakes and rivers.

Historical data is rarely found in the form of cave drawings. Most of the available data comes from written records and documentation, which are mostly restricted to regions with a long tradition of writing, such as Europe and Asia. Written historical documentation can take the form of logbooks or harvest records. At best, logbooks are simple descriptions of weather and wind conditions, and harvest documentation often only describes spring and summer temperature anomalies. Therefore, historical data has some limitations, but when a large amount is compiled, it can complement natural climate proxies, allowing us to reconstruct climate fairly accurately.

Although historical records have limitations, such as regional bias and incomplete data, they are still valuable supplements to natural climate proxies. When carefully compiled and interpreted, these human-made sources enrich our understanding of past climates by offering insights into environmental conditions and how societies perceived and adapted to them. Science and history form a powerful partnership in tracing Earth’s climate journey.

1. Disclaimer: This blog entry is the second part of the A Journey Through Time series ︎
2. Image taken from: García-Herrera, R., García, R. R., Prieto, M. R., Hernández, E., Gimeno, L., & Díaz, H. F. (2003). The use of Spanish historical archives to reconstruct climate variability. Bulletin of the American Meteorological Society, 84(8), 1025–1036. https://doi.org/10.1175/BAMS-84-8-1025 ︎

The post A Journey Through Time: Reconstructing Earth’s Climate from History appeared first on Global Change Ecology.

Nature as a climate witness:

Hints on earth’s past climate are hidden everywhere, we just have to know how to find and interpret them. Some of the most fascinating sources used for climate reconstruction come from the most unexpected sources. Tree rings and ice cores are natural archives which can store historical climate patterns in the form of different physical characteristics. By analysing those physical properties scientists can unveil  temperature shifts, precipitation levels and atmospheric conditions. Tree rings show us annual growth trends influenced by climate while ice traps tiny air bubbles that capture the atmospheric conditions of the earth’s past. When taking a deeper look at nature, we can find many more proxies usable for climatic reconstructions. Marine sediments, fossils, lichens, glacial features like moraines, and sedimented pollen are only a few further examples. 

The fact is that if you really want to use natural sources for climate reconstruction, you have to think outside the box and delve deeper. Using annual growth trends or ice cores as climate proxies may sound straightforward, but it’s more complex than you might think.

Let me briefly introduce you to the science behind these ice cores. As well as analysing the content of past greenhouse gases, ice cores provide layers that can be examined. Similar to tree rings, these are formed by seasonal differences in temperature or extraordinary events such as volcanic eruptions. These boundaries are clearly visible in the upper layers and can be used to determine the age of the ice. The thickness of these layers can tell us about precipitation rates and temperature, which are important climate indicators. With the help of geochemists, even deeper ice sheets can be studied. Different oxygen and hydrogen isotopes transfer climatic information.

Figure 1: An ice core drilled from the West Antarctic Ice Sheet Divide project, containing a dark layer of deposited volcanic ash Credit: H. Roop, National Science Foundation

Three common isotopes are found in Antarctic ice: H₂¹⁶O, which makes up almost 99.7% of the precipitated snow, and two rarer ones: H₂¹⁸O and D₂¹⁶O. Changes in the concentration of these isotopes indicate changes in temperature because the proportion of H₂¹⁸O and D₂¹⁶O is linearly and consistently related to temperature in Antarctica. During colder periods, the H₂¹⁶O content of ice is higher. As the climate warms, the proportion of H₂¹⁸O in Antarctic ice cores and the proportion of H₂¹⁶O in oceans increases. The same reasoning can therefore be applied to the analysis of foraminifera, which are shelled microorganisms which trap oxygen in their shells as they form.

1. Disclaimer: This blog entry is the first part of the A Journey Through Time series. ︎
2. Image taken from: https://www.ncei.noaa.gov/news/what-are-proxy-data ︎

The post A Journey Through Time: Reconstructing Earth’s Climate from Nature appeared first on Global Change Ecology.

As part of the comprehensive course Natural Climate and Human Impacts on Climate, given by Professor Dr. Wolfgang Buermann of the University of Augsburg, this series of entries are a compilation of a seminar on the fundamental mechanisms of planetary climate, methods for reconstructing past climates, current consequences of global climate change, and other relevant topics.¹

What is driving the observed vegetation dynamics?

A complex interplay of biophysical and anthropogenic drivers shapes vegetation dynamics across the globe. Several key factors contribute to observable changes in vegetation patterns, growth rates, and ecosystem composition. The most significant drivers include climate change, CO₂ fertilization, changes in land use, nitrogen deposition, and natural or human-caused disturbances.

Climate change alters the structure and functioning of ecosystems by extending growing seasons, shifting ecological zones, and increasing drought stress. These changes impact regions differently, influencing both productivity and vegetation resilience.

CO₂ fertilization enhances photosynthesis and plant growth, particularly in temperate regions where water and nutrients support this physiological response. While this effect may temporarily increase biomass, its long-term sustainability is uncertain.

Changes in land use, such as deforestation, agricultural expansion, and afforestation, directly alter vegetation cover. Deforestation contributes to vegetation loss and carbon emissions, whereas afforestation and agricultural land management can result in localized increases in greening.

Nitrogen deposition, largely resulting from industrial and agricultural activities, can stimulate plant growth by enriching the soil with nutrients. However, excessive nitrogen input can disrupt the balance of ecosystems and reduce biodiversity, leading to unintended ecological consequences.

Disturbances such as wildfires, pest outbreaks, and disease events increasingly affect vegetation dynamics. These disturbances result in direct vegetation loss and alter successional trajectories and species composition.

Figure 2: Attribution of Trends in Growing Season Mean Leaf Area Index
(a) Trends in global-averaged leaf area index (LAI), derived from satellite observations (OBS), attributed to rising CO₂ (CO₂), climate change (CLI), nitrogen deposition (NDE), and land cover change (LCC) from 1982 to 2009 (Ref. 11).) (b) Contribution of different drivers to LAI change in latitude bands (>50°N, 25–50°N, 25°S–25°N, and >25°S) (c) Spatial distribution of the dominant driver of growing season mean LAI trend, defined as the driver that contributes most to the increase or decrease in LAI in each vegetated grid cell.

Ramifications

Global greening has measurable impacts on climate systems, the carbon and water cycles, and human activity. It enhances photosynthesis, thereby increasing plant productivity and carbon uptake. According to satellite data and Earth System Models (ESMs), this terrestrial carbon sink offsets approximately 29% of anthropogenic CO₂ emissions, equaling about 2.5 ± 1.0 petagrams of carbon annually. Additionally, seasonal CO₂ patterns have shifted, with earlier spring uptake and autumn release in the Northern Hemisphere, indicating changes in the timing of carbon exchange.

Greening intensifies evapotranspiration (ET), which increases the transfer of water vapor from the land to the atmosphere. This can reduce local soil moisture and runoff, raising the risk of drought, though it may also increase precipitation downwind. Early-season greening can deplete soil moisture before summer, which suppresses vegetation growth and increases the likelihood of heat waves.

Temperature effects vary regionally. Increased ET cools the land surface; however, greener vegetation lowers albedo, absorbing more sunlight and warming the surface. The global net effect is modest cooling, though the balance between these forces varies by location.

Socially, greening can support agriculture by extending the growing season and increasing biomass. However, reduced water availability and greater climate variability may threaten food security in vulnerable regions. These interconnected effects underscore the importance of viewing greening not only as an indicator of ecosystem health, but also as a catalyst for complex environmental and socioeconomic change.

Global greening is a powerful indicator of how vegetation dynamics are reshaping Earth’s systems. Yet, the full scope of its long-term consequences remains uncertain. As vegetation patterns shift in response to climate, land use, and atmospheric changes, so too do the feedbacks that influence global temperature, water availability, and ecosystem stability. Continued research and improved monitoring are essential to deepen our understanding. Importantly, integrating vegetation data into climate policy and land management strategies can help guide adaptive responses—supporting sustainable agriculture, biodiversity conservation, and carbon mitigation efforts in a rapidly changing world.

References

1. Chen, C., Park, T., Wang, X. et al. (2019) China and India lead in greening of the world through land-use management. Nat Sustain 2, 122–129. https://doi.org/10.1038/s41893-019-0220-7
2. Gaspard, A.; Simard, M.; Boudreau, S. (2023) Patterns and Drivers of Change in the Normalized Difference Vegetation Index in Nunavik (Québec, Canada) over the Period 1984–2020. Atmosphere 2023, 14, 1115. https://doi.org/10.3390/atmos14071115
3. Piao, S., Wang, X., Park, T. et al. (2020) Characteristics, drivers and feedbacks of global greening. Nat Rev Earth Environ 1, 14–27. https://doi.org/10.1038/s43017-019-0001-x
4. Wang JA, Sulla-Menashe D, Woodcock CE, Sonnentag O, Keeling RF, Friedl MA. (2020) Extensive land cover change across Arctic–Boreal Northwestern North America from disturbance and climate forcing. Glob Change Biol. 2020; 26: 807–822. https://doi.org/10.1111/gcb.14804

1. Header image taken from: https://www.wikiwand.com/en/articles/vegetation ︎

The post Academic Series: The Science Behind Vegetation Dynamics (part II) appeared first on Global Change Ecology.

How do we observe global changes in the vegetation cover of the planet?

This question is covered by a relatively new area of climate research that seeks to understand how plants respond to rising temperatures, shifting weather patterns, and changes in atmospheric composition caused by global climate change.

Since 1981, technology has given us the ability to observe global vegetation, when the Advanced Very High Resolution Radiometer (AVHRR) was installed on the NOAA-N spacecraft. This sensor could take pictures of the Earth beyond the visible spectrum; it was highly sensitive to near infrared, but could not sense the blue range. More advanced sensors, such as MODIS, added the blue range to the picture.

The collected data is analyzed using indices. The two most popular indices are the Normalized Difference Vegetation Index (NDVI) and the Leaf Area Index (LAI). The NDVI shows the ratio of the difference between the amount of light reflected and absorbed in the near-infrared and visible spectra. Healthy green foliage absorbs most of the visible spectrum and reflects more than half of the infrared spectrum. The higher the NDVI index, the greener the surface. LAI measures vegetation density by comparing total one-sided leaf surface area to ground area covered (m²/m²). Monitoring helps track vegetation trends, estimate evapotranspiration, and forecast agricultural yields.

Several important metrics are commonly used to assess vegetation dynamics and ecosystem responses. These include SOS (Start of the Growing Season), which marks the beginning of active plant growth, and EOS (End of the Growing Season), which indicates the decline of vegetation activity. LOS (Length of the Growing Season) represents the duration between SOS and EOS and provides insight into seasonal shifts influenced by climate change.

Primary productivity, measured as gross primary productivity (GPP) and net primary productivity (NPP), reflects the overall carbon uptake by plants. GPP refers to the total amount of carbon fixed through photosynthesis, and NPP represents the portion remaining after respiration, serving as an indicator of biomass accumulation and ecosystem productivity.

What do we observe in vegetation dynamics?

Although data obtained earlier from the AVHRR sensor may be less ideal for long-term analysis due to internal limitations, calibration in combination with data from more modern sensors clearly shows a distinct global greening trend since at least the 1980s. Piao et al.’s study³ indicates that, from the 1980s to the 2010s, leaf area increased by 5.4 million km², equivalent to the area of the Amazon rainforest.

However, trends vary when scaled. In certain regions, reverse dynamics, or browning, may be observed. It is also possible to identify greening hotspots. Seasonal shifts are also observed. The growing season is starting earlier and ending later, effectively extending its duration. Peak greenness is occurring earlier and becoming more pronounced. Seasonal patterns of vegetation greenness are shifting. High-latitude regions are showing reduced seasonality, with patterns similar to those of regions farther south in the past. The start and end of the growing season are moving northward faster than peak greenness. These changes have implications for the agricultural sector and ecosystems, which will be explored in the following sections.

Greening Hotspots

China and India have emerged as key contributors to global greening, albeit through different pathways. In China, 42% of the greening is attributed to forests, while 32% is attributed to croplands. This greening has been driven by large-scale afforestation and reforestation programs, which have increased forest cover, reduced land degradation, and enhanced carbon sequestration. However, these efforts have also placed additional pressure on water resources. Meanwhile, agricultural productivity rose by 43% from 2000 to 2016, supported by multiple cropping, irrigation systems, and intensive fertilizer use. In contrast, 82% of India’s greening is cropland-based, with only 4% stemming from forests. This trend is largely the result of agricultural intensification, which led to a 26% increase in cereal production over the same period through expanded cultivation areas and intensified farming practices, similar to China’s approach.

In the case of Arctic regions experiencing greening, agricultural fields and afforested territories are no longer the main contributors. In these regions, vegetation covers the land due to natural growth, primarily through shrubbery. Gaspard et al. refer to this phenomenon as “shrubification.” In their study, the methodology included working with indices, overlaying vegetation maps, and mapping the types of cover and surface deposits in the studied region using ecological models. This allowed the authors to determine the role of plant communities and zonal dynamics in the observed phenomenon.

Recent greening trends in the Arctic and boreal regions reveal significant changes in land cover. Currently, approximately 13.6% of the region has experienced land cover change, and if this pace continues, the entire area could transform within 200 years. In boreal forests, the net loss of evergreen cover coincides with an increasingly active fire regime. In Arctic areas, the gradual expansion of shrubs is more difficult to detect, yet it contributes to the overall greening. Additionally, there has been southern herbaceous growth, primarily driven by extensive agriculture in regions such as Alberta and British Columbia. However, this gain is largely seasonal and linked to agricultural cycles. It should not be interpreted as a long-term ecological shift, such as the more persistent vegetation changes occurring in the Arctic.

Please, stay tuned to know more about what drives vegetation dynamics and what are its ramifications.

1. This is the first entry on the series ︎
2. Header image taken from: https://mpimet.mpg.de/en/research/independent-research-group/climate-vegetation-dynamics ︎
3. Piao, S., Wang, X., Park, T. et al. Characteristics, drivers and feedbacks of global greening. Nat Rev Earth Environ 1, 14–27 (2020). https://doi.org/10.1038/s43017-019-0001-x ︎
4. Statistically significant trends (P ≤ 0.1, Mann–Kendall test) are color-coded. Gray areas depict vegetated land with statistically insignificant trends. White areas depict barren land, permanent ice-covered areas, permanent wetlands, and built-up areas. Blue areas represent water. The inset shows the frequency distribution of statistically significant trends. The red circles highlight the greening areas, which mostly overlap with croplands except for circle number 4. Similar patterns are seen at P ≤ 0.05, and the seven greening clusters are visible at P ≤ 0.01. ︎

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