Beyond Mean Climate: Quantifying Climate Variability and Extremes under Varying Boundary Conditions

地球气候可以广义地用两个概念来定义，平均值和围绕这些平均值的变异性；例如，某个地点在某个间隔内的平均温度，以及在任何给定的日、月、年或十年，温度与该平均值的差异有多大。这种变化性对人类社会很重要，会导致极端热浪或干旱等现象。在地球漫长的历史中，平均气候发生了深刻的变化。例如，2万年前，地球平均温度低约5摄氏度，大冰川覆盖了今天没有冰的大陆的部分地区。我们知道平均气候已经改变了，因为我们有来自自然档案的证据，比如在两极仍然冻结的冰的化学中发现的证据。但这种可变性是如何变化的呢？变异性是否以与平均值相同的模式变化？在过去，极端事件--如极热或极冷的温度--在不同的时间发生一次？每年或十年之间的变化，比如2万年前的记录，都是极其罕见的。我们将使用格陵兰岛和南极洲古代极地冰的非常高分辨率测量的气候记录，通过一种被称为“冰芯”的过程来研究地球气候的内在变异性以及它如何在很长一段时间内发生变化，从时间上追溯到现在之前的10万年。气候的这些方面、可变性和极端，除了平均气候之外，还可以提供新的背景，帮助我们更好地理解我们不断变化的地球。平均气候与其内部可变性之间的关系是气候动力学的一个基本方面。了解内部变异性对平均状态的依赖关系，对于了解气候强迫变化的可测性，以及极端事件发生可能性的变化至关重要。关于地球历史上内部气候变化的信息非常罕见，因为平均气候经历了巨大的变化，例如大约20,000年前的最后一次冰川盛期。大多数古气候档案缺乏细节或连续性，无法可靠地解析数万年的年度、年际和年代际时间尺度。我们将使用一套由水同位素和尘埃等杂质组成的五个极高分辨率的冰芯记录，从统计上对极地气候的变异性和极端情况及其与背景平均状态的关系进行分类。我们将研究稳定的平均气候、全球平均气候的长期变化以及气候突变时期的这些关系，并对高频、高纬度气候变异性提供前所未有的分析。这项分析将跨越最后一个冰川-间冰期周期，时间追溯到过去的10万年。在整个历史上，高频气候变化一直对人类和社会产生影响。年度、年际、十年和百年尺度的变化推动了宜居性的变化，导致了过去文明的繁荣和崩溃。极端气候事件尤其影响现代生活质量、国家安全、食品和水的可获得性以及生态系统服务(除其他关切外)。关于过去气候变化和极端的拟议研究，以及与平均气候的关系，可以提供新的背景，帮助我们更好地了解我们不断变化的地球。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The Earth’s climate can be defined broadly by two concepts, average values and variability around those averages; for example the average temperature of a location over some interval and how much the temperature varies from that average on any given day, or month, or year, or decade. This variability is important to human societies, driving things like extreme heat waves or droughts. Over Earth’s long history, the average climate has changed in profound ways. For example, 20,000 years ago, the Earth on average was about 5 degrees Celsius colder, and large glaciers covered parts of continents that are ice free today. We know that the average climate has changed because we have evidence from natural archives, such as that found in the chemistry of ice that remains frozen at the poles. But how has the variability changed? Does the variability change with the same pattern as the average? How often do extreme events - such as extremely hot or cold temperatures - occur at different times in the past? Records of the year–to-year or decade-to-decade variability, say from 20,000 years ago, are exceptionally rare. We will use climate records from very high-resolution measurements of ancient polar ice in Greenland and Antarctica, obtained through a process known as ‘ice coring’, to study the inherent variability in Earth’s climate and how it changes over long periods of time, extending backwards in time up to 100,000 years before present. These aspects of climate, the variability and extremes, in addition to the average climate, can provide new contexts that help us better understand our changing planet.The relationship between the mean climate and its internal variability is a fundamental aspect of climate dynamics. Understanding the dependence of internal variability on the mean state is key to understanding the detectability of forced changes in climate and, critically, the change in likelihood of extreme events. Information about internal climate variability throughout Earth’s history, as the mean climate has undergone large changes, such as during the Last Glacial Maximum about 20,000 years ago, is exceedingly rare. Most paleoclimate archives lack the detail or continuity to reliably resolve annual, interannual, and decadal timescales for tens of thousands of years. We will use a suite of five extremely high-resolution ice core records of water isotopes, as well as impurities like dust, to statistically catalog variability and extremes in polar climate and its relationship to the background mean state. We will examine these relationships over periods of stable mean climate, long term changes in global mean climate, as well as abrupt climate change, and provide an unprecedented analysis of high-frequency, high-latitude climate variability. The analysis will span the last glacial-interglacial cycle, extending backwards in time up to a 100,000 years into the past. High-frequency climate variability has been impactful to humans and societies throughout history. Annual, interannual, decadal, and centennial scale variability has driven changes in habitability leading to the blossoming and collapse of past civilizations. Extreme climate events in particular affect modern quality of life, national security, food and water availability, and ecosystem services (among other concerns). The proposed research on climate variability and extremes of the past, and the relationship to average climate, can provide new contexts that help us better understand our changing planet.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.